| Are these the same as the carby 900ss mirrors?
If so they are glued in with couple of blobs of putty like stuff. Bit like a sticky mastic. One of mine used to detach itself at the outside edge when the weather got cold.
You could heat up the glass with a hair dryer and slip a bit of wire with a right angle bend at the end of it between the glass and the plastic housing. By rotating the wire so that it catches you might then be able to separate the mirror from the glue.
Can't you just mask off the glass? It would be a lot safer than breaking the glass. | 
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