You could try an RCC1 & Varilock spacer as I use successfully:
https://www.flickr.com/photos/247194...in/photostream
Yes - you can remove the nosepiece to get more back focus
but you'll require more power to get to the same temperature as
the peltier cooler will be heated up by the air in the filter wheel.
By the way - the QHY9 is not sealed -
there are gaps all around the connectors.
Only the internal chip has a sealed window with dry Argon gas inside.
cheers
Allan