Joined: Oct 2008
Posts: 1,619
Likes: 187
From: Frankfurt, Germany
Bikes: Focus trash find commuter, Eddy Merckx Corsa, BP Stealth TT bike, Leader 720 TT bike, Boardman Comp Hybrid drop bar conversion, Quantec CX budget cyclocross build, SerottaNOS frameset ready to build up!
I´m 99.99% sure you know about P-clips (and those funky seatpost clamps with the rack mount holes), and that you have decided against using them, but am mentioning them nonetheless.
Best of luck, and apologies if I am pointing out the bleeding obvious.
By the way - steel P-clips are stupidly strong, so worrying about them breaking is not really an excuse not to use them. Not directed at the OP, by the way.