Is there any way to turn on just elevation for support in isometric?

There is but it will affect other coordinate call outs also. Firstly set your coordinate output for supports = true. This is OS:5 if not mistaken.

Then in alternative text you can suppress the northing and easting call outs. This will then just give you elevations on supports.

Hm, nice approach, but I need coordinates at other components..
I will disable coordinates for support and add Elevation in TAG. But in that case that text will be in Tag box frame.
I know that we can split text in second row with $ character, I wondering is there a way to tell him to do it text with box or without.