By providing nest materials for bumblebees and stingless bees either indoor or outdoor environments.

I have no idea for stingless bees and bumble bees. For other bees like leafcutting and carpenter bees it could be recommended put some tubes which will help to be used as a nesting material for bees. I used this way to increase the number of Megachile and Osmia for alfalfa pollination. 

Good luck with your research 

Possible resources that would be of use:

http://www.xerces.org/books-managing-alternative-pollinators/

http://www.xerces.org/wp-content/uploads/2008/10/agroforestrynotes34-bee_nests.pdf

Thanks to all for the useful links and guidance