Hmm, well, I had the idea of Shinji ordering the demons to capture the other FSN characters (or, at least, the female ones...) and them being unable to do so. So, in order to avoid his wrath, they instead have some demons impersonate Sakura, Rin, Rider, Saber etc., and hand them over to him. He would then proceed to rape and torture them as he would if they were the real girls, whilst the real girls are still happily walking around ready to thwart his plans (and fucking Shirou etc...).
I think that would be rather amusing....
As for the two ideas more generally, I really need more context to come up with scenes (especially non-BDSM scenes). The ideas are just too broad right now, so we need to work out a plot etc. to fit the scenes to.