This may not work for all T-bars, but it has for mine & cost less than $1
1. Remove one mic mount from the T-bar by unscrewing
2. Screw in a piece of 3/8" threaded rod about 3-4" long into the hole on the T-bar & add a nut & washer to each end. To be used as locking nuts.
3. Screw the shock mount onto the top of the threaded rod & use the locking nuts to adjust the height you require.
The extra length you leave on the piece of threaded rod allows you to adjust for using windscreens. You could also achieve the same result by using 3/8" bolts with thread all the way to the head. Two different length bolts for windscreens or without. I prefer this way as I had the parts laying around & it is fully adjustable.
Sorry about the blurry photos, but you get the idea!!