Thanks for the suggestions, for the record, off-list I received a couple of tips 
to try with UV-curing optical adhesive. I'm not sure if I can find any locally, 
and I'm not sure I can wait the three months it would take to arrive from the 
States, but I had a hunt around and Norland Products 
(www.norlandproducts.com) seem to offer a wide range of different options.

I hope this is of use to the list in general, thanks to all who replied.

Saludos

Chris Wood
Instituto de Biotecnología
Universidad Nacional Autonoma de México