Hello,here is my solution:
I open a small window on the engine mount with a dremel tool(or similar)
http://www.rctech.net/forum/attachme...1&d=1328654604

small enough to fit tight a M3 nut
http://www.rctech.net/forum/attachme...1&d=1328654779

then you just screw the engine as tight you want on the mount
http://www.rctech.net/forum/attachme...1&d=1328654932

Hope this will help someone that's why I posted it.