Thank you all for your replies, they've been very helpful in thinking about this.
I'm pretty sure my rowing is smooth, I used to row in college, and remember having the same problem with the model Cs. I think the straps loosen at the catch (when my feet are bent), not at the finish. Of course you are all right in pointing out that the smart thing to do would be to attempt to fix the strap problem (like getting the new thicker straps, or double-looping), but now that I've had my crazy idea, smart alternatives are out the window
I really like the way the shoe setup on a boat feels. I'm thinking on the erg it would be kind of like using clipless shoes on a bike - sure, regular pedals work fine, but clipless makes you one with the machine.
The reason I was thinking of using a plate is that I'd really rather not drill through the footplate, especially considering that there are already four convenient holes pre-drilled into each footplate for the current binding system.
My first idea, then, was to use the four existing holes to attach the plate that the shoe is attached to, perhaps using wingnuts to make it easier to take off.
Unfortunately, I ran into a very important constraint - my wife uses the erg all the time as well, and although she's onboard with the idea of using shoes instead of straps, she's not too keen on the prospect of having eight wingnuts to unscrew and screw back every time we change between my shoes and hers.
So now I'm going crazy trying to find someone that manufactures a quick-release system for attaching shoes to footstrechers, which would solve my problem since I could just leave the quick-release fixed to the erg and easily change between different shoes.
I've only been able to find one product that I think might work (emailed them but haven't gotten a response yet):
rowfit.com/fas.htm
I even thought of modifying a professional camera tripod quick-release plate system, but I think the forces involved would be too much for those plates to bear.
Anyone know of any quick-release systems that could work? I'm sure
someone must make quick-release boat shoes, I just need to find out whom...