trek pole grips and using two poles for 6′ tent pole

I have not tried that, but I know how sensitive my hands are to roughness in the pole grips – and I am a guy who works with his hands, so mine are not the most delicate hands. I'd guess that if I made an indentation I'd have to round it off so much in order to be comfortable for my hands that it would not function effectively in terms of helping to align/interlock the poles in tent pole mode.
Have you considered, instead, mounting something on the shaft of the poles that would cradle the handle in pole mode? that would not affect the grip at all.

have a look at this ready made converter :


http://www.blackdiamondequipment.com/en-us/shop/mountain/shelters/pole-link-converter

Willy did a post using tubular webbing and Velcro straps to connect two poles together– genius:

http://www.backpackinglight.com/cgi-bin/backpackinglight/xdpy/forum_thread/17864

I use rubber bike inner tube cut to length needed, stretchy, holds like a rock, and very adapatable to any dual pole combination you want to put together.