Hi

You can try to using apeizon wax - grade W. This softens at 85
degree Celsius. You may need to come down a bit with KOH bath temp.
http://www.sisweb.com/vacuum/sis/apzwaxes.htm I have came across a paper,
where they have used this successfully. It is also possible to use LPCVD
silicon nitride thin layer. You can think of using fixtures from AMMT -
http://www.ammt.com/content/products.html

Hope this helps you.

amod