Hi Thom, I didn't mean to detract from your fine pen. There are many examples of modifications of slims. Yes, I simply dill a 7mm hole in a scrap that is about 1/2" thick, part the initial upper slim blank down to the tube (about 1/4" now exposed), and glue the scrap on the end. Now you have 1/4" with no tube in. Turn the lower blank to whatever profile you want, then measure the end that will meet the upper blank (OD), and drill out that 1/4" overlap to allow the lower section to go into the upper section.
Don Ward wrote an entire book on how to do modified slims. This is certainly not my idea.
Once you get the hang of the centerbands, continue and do some closed ends, with different simple segments.
My point is, your slims are great kits - Have fun!