disable single option in s:radio

[Stephan Eimer]

I googled a lot around but couldn't find the answer to the question: how to
disable a single option / choice in a s:radio tag? It should look like this:

- option 1
- option 2 (should be disabled)
- option 3

The list of options comes from an enum and is displayed correct. The
standard s:radio disabled parameter offers only disabling the complete radio
list. Any ideas how to realize it?