Trillspanner line thickness

[Jonathan Wilkes]

Hello,
     I'm getting to the end of formatting a score, and I just need some 
hints on changing the thickness of the zigzag line after trills.  I've 
tried zigzag-width, thickness, and everything else that looked promising 
but with no results.  I didn't use font-size because I want the trill sign 
to stay the same size.

     Is what I want to do possible?

Thanks,
Jonathan