Attached a pic of the secondary holder. The adhesive took a few days to cure fully and I would be very surprised if a heater could affect it. The silicone is pretty tough and you would need to be able to get at it with a scapel to free up a mirror - a solid back plate would be a problem (but that will also produce cooling issues). It would also be difficult to clean it off completely from a mirror, but it should be possible to get most of it off with a blade (maybe try some out on window glass).
I was also concerned as to how I could align the major axes, but found that it was possible to get good alignment by eye - I just marked the desired offset longitudinal position of the support on the back of the mirror and then moved the support around until everything looked symmetrical when it matched the mark. maybe I got lucky, but it really wasn't difficult at all.
I guess your primary mirror is fairly thin if PLOP shows significant errors on a 3 point mount. Even with 6 point, glueing onto the support points might be worth considering to get around the edge support issue. The standard Dob edge supports are fine if "down" always has the same alignment to the OTA - but of course it doesn't with an EQ mount and you will always have residual (and varying) astigmatism from non-optimal edge mounting. I found out how bad an imperfect edge support can be when I accidentally set up my 12 inch Newt with an edge support directly under the CofG and taking much of the weight of the mirror - the astigmatism was horrendous and way worse than anything arising from a glued mounting (which is its normal situation). The discussion on
http://www.cruxis.com/scope/mirroredgecalculator.htm seems to be on the money and well worth a read if you haven't already come across it.
regards Ray
added comment: I just looked up Rolf's description of his scope - he used 3 silicone blobs to mount his 10 inch primary