Hi,
I would use a 2 pack epoxy resin. It comes in 2 tubes, you mix equal parts of each, and it starts to set within about 5 mins or so. You can get a 'clear' version which sets completely clear. There may be other types of adhesive which are suitable, but this sets fast so you don't have to hold it in place for a long time.
The other option would be to use RTV silicone, but again, this takes a while to set, and should not be used in contact with circuit/solder joints etc since it releases acetic acid during drying.