I think a fall crop of Rapeseed would kind of like a "candy crop" - Similar to cowpeas or soybeans fall planted. It just won't have time to mature with a fall planting.

Rape does really like Nitrogen though - so if you have a good amount or can add it - you might have a small, attractive plot come October.

I'd probably mix in some Wheat, Rye or BFO to help keep the pressure off the young rape - so it can get at least some size by the first frosts - which will kill it.