well the best approce is going to be the difficult one
that is get a bolt and drill a hole but not all the way the to the end and put prob in hole and use nut to mount it inside the hlt with a rubber or silicon washer
the heath robbison way would be to drill a hole just undersized and then silicon around it ( I wouldnt trust that way on a hlt though)
you can look for the bolt type thing or get someone witha lathe to make one for you