I've worked in several consulting organizations (from Global Systems Integrators to Boutique specialty firms) and, in general, consultants who also have business development responsibilities have a multi-part comp plan that, as you mention, you want to design to incentivize the right behavior. Here are some components to think about:
1. Utilization against target (this is the basic incentive to drive billable hours). So if you set an 80% utilization rate, and the consultant meets or exceeds, that's one part of their bonus (this is the meat and potatoes);
2. Team or group utilization for managing consultants (to help make sure the senior consultants are keeping the more junior ones applied);
3. Business dev bonus - based on net revenue (this helps the consultants keep margin front-of-mind, comp is based on revenue net of cost of service and any quality concerns/unpaid invoices). You can split this into 2 parts: net new clients and/or existing client expansion - depending on what your goals are; and
4. Profit share - again, based on net margin, for the firm as a whole.
The trick for introducing a new comp plan based on business development is to make sure consultants don't take their eye off of the real reason they are there: providing quality services (utilization) to clients. So you can add in some caveats to each part of the bonus. For example, you can't earn your business dev. bonus if customer sat is below a specific measure (Net Promotor score, for example). Or you can't earn your biz dev bonus if your utilization is below 70%.
Then you put a plan in place and set the expectation that you will adjust the plan accordingly each quarter until you get the behavior and results you want.
I would also recommend Daniel Pink's book "To Sell Is Human" to help consultants get over the stigma of "sales person."
Hope this helps.