If you have the single servo mount, ( remember that I may not have seen exactly the same configuration you are talking about... ) then cut out the covering from where the servo will go. Do not cut the surrounding wood.

Glue two small ply rectangular shaped thin "blocks" where the servo screws would go, and let dry.

Then drill and screw the servo screws into these blocks to hold the servos in place.

Re: Hardwood.

Could you post a picture of the part you are talking about?