The trick is a paralyzed scrib above the roof, with an attached script to immediately attack the player and start playing the morrowind title one second later. For some reason the one second delay was required for this to work (on my old and slow computer, the regular battle music didn't start within this second). As the scrib is already attacking the player, no further attacks will retrigger battle music and the morrowind theme may play uninterrupted, no matter how many dremoras you console in to the cell.

In this plug, random battle music will start once the morrowind title has played through, but this should be possible to fix with another timer.
I admit that this is probably not a very elegant way to do it, with the extra creature outside the room, but it works. Could a clumsy idea like this be used? Any good ideas of how to make it more elegant? Any other good ideas of how to avoid battle music?