Alternatively - if you don't mind the cost of buying a new house like the one below - it could replace the ramp and sand bath altogether and make a new shelf. I've used this house for our syrians and they always move into it
The front left compartment is nice and big for a nest and it's the darkest area. The back centre compartment fits a litter tray and they seem to like having their toilet there, next to their nest.
It's not cheap though and it would need to be supported underneath in case tunnelled under as could squish the hamster. They do sell legs for it but if you didn't mind a bit of diy you could just glue some dowels on for legs. Although it's wood, you can just paint the inside with plastikote and then it's wipe clean. My first one I didn't paint and although the toilet area did get a little bit of staining in the long term it just scrubbed clean. But if plastikoted it's just wipe clean. I just do the inside - the outside stays fine.
But you may not want to spend all that for an older hamster ....A shoebox house would be fine too if it's large enough for a big nest and also fit a litter tray. And that's light so would just sit on top of the substrate.
Rodipet® Hamster House Maze DaVinci 41x26 cm, Ø 7cm +terracotta