There is a product made called "Foto Frisket". It is a clear material that is sticky on one side.
You can put this on the canopy and cut it gently with a #11 blade around the frames.
The adhesive is low tack so paint won't lift off. It comes in a 10 pack with sheets that are 8x10 inches. So one pack will last a long while and can do any canopy that you may do on any aircraft.
If all else fails you could also use little strips of painters tape as well..
Hope this helps
Paul