I might be of some help in this area. If that's a U-lock on the there (not sure). I know a silent but deadly technique for opening them up. Involves a car jack. I've done this on two of my own locks (lost the keys) and it only took 5 mins. on one and 10 on the other. We take some tools along (exact right wrenches for all moby large nuts) in case it's easier to remove what it's locked on and move in and out as silent as a ninja whispering to a gnat.
I don't think it's a good idea if you lock up the bike with our own chain. Just alerts him to our presence. That when the trap gets sprung.
The cover of a rainy night might be perfect; he won't be riding, and the rain will cover up some of the noise.
I'd love to come along.