You could possibly elongate the hole and fit bullet connectors through. But.. For the price of a stock pipe and its hardware, you will have resolved the problem and can use whatever connector you favor.
The following is the stock pipe/buffer tube that I currently have on the Katana and works perfectly. The aluminum spacer/stopper that comes with the stock pipe, needed to be reversed when placing it in the stock pipe/buffer tube and the area around the screws hole, needed to be ground off. By doing this, I was able to get the right amount of threads into the cylinder's spacer and not have any threads protruding into the receiver.
http://airsoftdepot.ca/catalog/produ...roducts_id=881