You pay a flat fee to WestLaw or LexisNexus, you charge your client an hourly fee for its use, or better yet, charge each of your clients the whole flat fee you pay to the service. That's what Chadbourne & Parke out of New York has been doing. Say they pay $100 per month for WestLaw and they have five clients. Chadbourne has been charging each client $100 per month for WestLaw use, so they get $500 for a service that in total costs them $100. They're making a profit off of charging for their costs!
Unethical? I'd say so. The article about it links above and it's got some pretty interesting bits aside from the always enjoyable silk-stocking firm slip up.