A way to play any song in the SoR1 ost in SoR2 through a jukebox in a bar that could randomly be in certain bar chunks. (or whatever method of getting it to appear in a bar with a low chance)
The song could only be heard in the bar or very close to it, and would be a nice callback to the first game.
All of this is only if it’s legal (within copyright laws) of course, but I do think it would be a fun secret if possible.