I think silicone thermal pads along with hollow hole punches could do the job.
I found some silicone pads in digikey. It is a little pricey(I am guessing you would need two of those), but whole lot less than type-s.
http://search.digikey.com/us/en/products/H48-2K-150-150-0.2-0/1168-1206-ND/3042035The pad is made of silicone, has thickness of 0.2mm, is without adhesives on both sides and has shore A measurement of 60A.
Also, here are hollow punches in different sizes:
http://store.harryepstein.com/merchant2/merchant.mvc?Screen=CTGY&Store_Code=1930&Category_Code=HolePunches(the video above says the diameter of cylinder shape measures about 8.4mm)
so, you might want to purchase 5/16", 6/16", 7/16" punch to try out. I am guessing 5/16"(7.94mm) and 7/16"(11.11mm) will be enough assuming the silicone pad stretches out a bit.
Hmm.. but this is a lot of investment for a mod. The mod will require two silicone pads, 8mm, 9mm, 12mm punching tools. Including shipping and all it would be something like $40 and the tools purchased are not likely to be used elsewhere, unless you have many Topre boards to silence. Finally there is no guarantee of success....