@johnconstantelo did something like this for a deadbolt. That and some other options are discussed in the following thread (along with some pictures). Just be aware that the thingshield is no longer available, but that’s only one of several options discussed.
I think the idea behind the suggestion of the sensative strip is that the magnet part is very small, and you might be able to put that on the moving part of the lock and then just put the long strip where you want the contact to be made. The strips can be painted, so they can be almost invisible on the door. It just depends if there’s enough space for the long piece.
With any two piece reed sensor. You can substitute any magnet you want for the magnet piece, it just has to be strong enough to move the reed in the other piece. So there are some options if you want to try to hide the magnet in some way.
Some people don’t care as much about the aesthetics and just want the result. Here’s one project report from a member who wanted a laundry alert based on the position of the rotary dial on the front of the machine. Again, a similar idea.
So that kind of approach might be possible, it just depends on exactly what there’s space for at the point where the bolt engages. But you’d have to be getting inside the door and it could get tricky.