Know-How Exchange : Strategy

I'd go with Adwords, using a high-conversion landing page and sophisticated targeting. Once you've proven it works (and generates qualified leads) you can expand into LinkedIn advertising.

And I'd be happy to take a closer look at how to implement and manage such an effort. Let me know if I can help you.

You write,"... they've been doing well, but want to expand in the area of Job-Fill".
Has the engineering firm done any market research to locate or quantitate the need for this service?
If they just "want to", it may be better to back up a step or two. If they have actually done some of this work, then they should find out how the client searched for vendors.

This "investigating" for new clients seems like market research.

Of all the options you list, LinkedIn would have the highest concentration of professionals. They should find some of the Engineering- and entrepreneur- related groups... join-up and become active. Some of that activity will take the form of asking questions and spurring discussion. This won't be blatant sales, rather, it will be investigation of the market. They should not hide the firm they represent, and they should illuminate their capabilities to help solve the issues being discussed. On LinkedIn, strive to become problem solving partners, not salespeople. Again, their aim is to investigate and assist. Investigation will naturally lead to other avenues of approach.

It is never easy to break into new areas but the trend to outsource functions is working for them. Nonetheless, it will take time to build the knowledge and trusted reputation (the Brand) required to attract good clients.

if there is an association or other similar organization that caters to the prospective clients' interests, may I suggest that you/your client consider ramping up efforts to become more involved with this org including conference speaking gigs, sponsorship, and other associated channels. this is a viable way to demonstrate expertise to an audience that commands you to convince them why you're so great, and you can accomplish this without transactional/CTA interactions such as cold calls.

so now, your client is placed in a position where they could showcase their support of the industry by developing educational programming at events/conferences and basically helping others. but getting back to audience scrutiny - you deffo need to train your client to avoid making any speaking gig an infomercial. conceptually, i would put together a "best practices" panel or a "new solutions" panel.

this is also a good way of bringing together great/like minds, which will provide your client an opportunity to observe first-hand what clients need, in addition to discovering what the competition knows.

Looks like you have 2 different sets of customers, and like need to treat them differently:

"Helping other engineering firms with their overflow"
You generally know who the prospect s are, and they probably know who you are. They just don't know your availability for Job Fill. I would focus on networking and trade groups. For example, at industry events, have folks talk about how they can do the Job Fill work. If appropriate speaking opportunity or byline article opportunity can be brought up on this, try it. Maybe a trade ad or trade show conference guide ad.

"Helping entrepreneurs"
This is a classic new client acquisition. You have to find the prospect and then get info about who you are and what you do to them. More broad marketing likely is needed. The AdWords suggestion would be good. Supporting entrepreneur events could also be good.

Could you spin out a consultancy mech engr business, and market it as such? That will help people to find the consultancy, rather than try to convince prospects that they can do "it all". It would also help to market the consultancy (list it in all the "usual places"). If they have the bandwidth, scan for large RFPs that are awarded to companies, and reach out to them with a marketing proposal (especially useful if you already have expertise in the subject matter).

I agree with Jay on this one. Without any hard data and only the anecdotal results from the clients efforts to go on, this "feels" like the market may be leery of outsourcing to a company they dont know, don't trust or perceive as a competitor.

The way around that would be to sub-brand. Conveniently this approach would also provide an escape hatch. If the endeavor does not pan out and it is a sub, then the primary brand does not take a hit.