It might be sensible to do the training in an aircraft fitted with deicing kit. You could do the exercise with the kit turned off, but have it there for backup in case you need it. I have a feeling that's about the only way you'd persuade an instructor to do it.
Of course, this doesn't have to be an official part of training - we could all hire an instructor to take us up to do it if we felt we were likely to be doing the sort of flying which would benefit from it. If anyone actually does this, do report back.
There's a danger, though, that it might lead people into thinking they can handle light icing, giving them a false sense of security and getting them into trouble.