So there is a chance, that we can make it easier to get your usecase covered.
As you can see from my posts, I first thought, it can't be done at all. Then i did think about to use the fields widget, which has its own template parameter, that is handled internally.
So the resulting "code" is a bit clunky, but it should work as a workaround. There may be better ways, but I couldn't find them. ... And I did try for about an hour, as the timestamps of my posts show.
-mario