Slims are easy.
1) drill hole without going all the way through.
2) glue the tube in
3) use a jamb chuck (in a jacob's chuch or scroll chuck) to turn it and calipers to size the open end.
Not too tricky
Cigars and sierras can be done too, but you have to make sure that whats grabbing the tranny is taken into consideration.
what engages the tranny isn't the tube in either, but a part of the finial. On the Cigar this piece can be pressed into the tube without modification, not sure about the Sierra. But since both use the same tranny size, a cigar finial could be used to activate a closed end Sierra. You just have to make sure you get the depth right when you press it in.
Yo-Yo Spin (Ed) has made some closed end Cigars and they are in his photos I believe.
Heres one of my single body closed end slims