Insulation, Radiant and Vapor Barriers - Insulating End Wall trusses

My garage was built with standard trusses all the way. no end wall trusses on the ends. So I have a problem. how do i insulate the end trusses? I have the bonus room trusses over my garage. the ends of the bonus room are insulated because the contractor tipped up a 2 x 6 wall to fill that end opening but where the attic space is the truss webbing is up tight against the wall sheathing so there is only 1 1/2" of depth that I coudl use to insulate. I was thinking possibly just taking 2" styro panels and attaching them but thats only like R5. The garage floor is radiant heat and so is the upper bonus room.
Thanks for the help.

You should frame out this wall to your desired width. Meaning to say if R-13 is being used in the rest of the wall area, then frame out with 2 x 4's, if it is R-19, then frame out with 2 x 6's. You want uniformity throughout the room.