Radiobuttongroupbykey set readonly

Hi!

How can i set only one or two radiobuttons in a radiobuttongroupbykey to readonly?

My problem is that i have a radiobuttongroupbykey with 3 buttons. The buttons are binded to

an attribute with 3 values. 0, 0.5 and 1. In some cases only one of these three buttons may be selectable.

Should i use three seperate buttons for this or is it possible to use the radiobuttongroupbykey?

Hope someone could help me!

Thanks!!