Custom User Property Fields Based on Group Membership?

We want to use Clarizen to manage a large stable of freelance writers and designers. In order to do this, it would be helpful to add a number of custom fields to the property cards of these users - and only these users.

Is it possible to tie the presence of custom fields to a user's membership in a certain group? In this case, I would create a "Freelance Contributors" group; the property cards of these users would display the custom fields.

At this point, I'd just need to know whether this is possible, the general approach required to do it, and where I might go to learn the necessary details.

If this isn't a practical approach, would tying these custom fields to a specific profile be the next best option? Thanks.