Free legal advice issue ... halfway house maybe? And use the material to market your services, push your site higher up the search engine rankings and boost your visitor numbers?
How about offering to do a limited number of free answers to specific legal issues (eg one a week or once a month) on the basis that the person asking for your help agrees to let you display on the site an anonymous version of both the issue and the expert's answer? This is similar to what I do for another careers and jobs site.
Worried or naïve callers sometimes include in their request information that identifies them personally or would jeopardise their situation if it became known to the wrong people. You'll need to carefully edit the callers' information and the experts' replies before displaying anything on your site to protect the interests of everyone concerned. I've had to remove, for example, personal information about enquirers' state of health, where they live, their family circumstances, their earlier employers and the rest of it.
Would you also need to run a security check on your site to ensure no information got leaked to anyone who shouldn't have it?