Hmm, I used to install DSS for a few of my 'must have it' clients back when they first came out. Keep in mind the cheapest system in those days was about $700.00. I was told then that indoor DSS was not possible and it was actually set-up inside my wholesale dist office because of a situation such as yours. The WS putz with it and could never get any signal unless they opened the window. This left me with the conclusion that they could not be installed indoors as the signal bounces off the glass pane.
This was quite some time ago so I thought i'd check for you (and me) and found that a few people have been able to get it to work indoors.
Here's the
link
WB
BTW, there was a ruling in regards to outdoor mounting of DSS dishs back in 00 or 01 from the FCC. Something to do with the legality of DSS dishs in apartment complexes. Not sure if it pertains to your case but thought i'd mention it.