Fiber tape can be rolled into a cone shape and put into the holes. Basically cut off a length of tape and roll it so that it forms the shape of a funnel then just put into the hole.
The fiber tape is the plastic type tape with the fibers running through it is what I have used in a previous life, but I am sure there are new and better products.
http://m.3m.com/wps/portal/3M/en_US/...t=rud&MDR=true