I think you've asked a "loaded" question here. Yes, there are probably many that could cut the smaller cups to replace your plastic liners - giving you that liberated driver scenario. However, it's getting quite hard to vouch for someone who can take this on. Personally, I'd check with techheromods.com or even Marty as you suggested. Both should be able to deliver. But, the issue that I see is that ideally, whoever you pick to do the work for you, will probably desire to have the cups in their posession so that they can make an accurate fitting inner cup that will work with your Bila cups and the liberated driver.
<whew>
Putting that aside, I have 2 pair of woody headphones. One is liberted where the drivers themselves are inserted directly into the cup. I also have a 2nd pair where the drivers are still mounted into the smaller plastic cups and then into the wooden cups. To tell you the complete honest truth, I really can't tell the sound difference between the two. If you're looking at spening $80 - $90 on cup inserts to mount your drivers in, I'd personally recommend investing your money into something else, or save some more money for a new amp or buy some music.
Just my .02