using variables in a custom mailto command

Okay here is the challenge. 

We currenly have a trigger at the end of a course that will launch our emial client, populate the send, subject and body with the information we require with one exception.  the user still is required to enter their unique ID information before hitting send.

it would be great if the we could collect the variable in the course which we know how to do, and then have it dropped into the url trigger that we put at the end.

any thoughts?