Passing Variable Parameters

I have two types of users. Lets call them User A and User B. There is one object, called a VO.

A User A can have many VOs

A User B can have many VOs.

Every VO only has ONE user A and ONE user B. The issue is, when I create a form to insert a new VO, I can only ever do it connected to either a logged in user A, OR a searched User B. After having created a VO with one connection, how do I set the other one?

Im thinking setting the user B from the form after having searched through a list of user Bs, and passing the user A connection through as a parameter since user A is the one that is signed in. Is there a way to dynamically pass in the user A connection, so that whoever is logged in is automatically connected to the new VO that was created? Right now with URL parameter passing I only see passed fixed values, like a specific name or number.

Any ideas would be great. Thanks.