I could be wrong, but I assumed he was asking about adding a bypass cap to the auricaps. So far, I don't think anyone has done this. I ordered some of the inexpensive sonicap gen IIs to try as bypass caps for the auricaps in my Classic Two, but haven't received them yet.
The clarity ESA caps would be a reasonably priced cap to try, and of course the more expensive sonicap platinums.