Competent frozen yeast cells

[SMER2 at med.monash.edu.au]

I see that Stratagene are now supplying competent frozen yeast cells for use 
in the yeast two-hybrid system.  Has anyone used them and more interestingly 
does anyone know how they make them?  I have been looking for a protocol to 
produce competent yeast cells that can be stored at -70 similar to E.coli.

Any hints or suggestions would be appreciated.