That's exactly what I've been doing, but he is so locked onto the treat, I don't think he even realizes what he's doing with his foot. Maybe it's because we've been doing a lot more shaping than luring lately, he is kind of distracted by the constant presence of the food so close to his face. I've tried just using an empty hand that smells like treats, and I've tried just getting him to target my hand or a target stick. He still turns his head so quickly after the click. Maybe I'll lose the clicker and just use "yes". Someone else mentioned the clicker being better for higher energy behaviors.
O.K. Question - How many supported limps is Brody doing? i.e. three before you click or more.
What I would do is get him to do a few supported limps (as many as he can manage) BEFORE clicking -then if he drops his paw after the click that's fine, he's done his limp albeit supported, and if he turns his head it's no biggy.
Not sure which type of Clicker you are using but if it's the box type, the sound is very loud when it's close to a dog's head. This may also distract Brody because it's hurting/uncomfortable. If that is the case, then deaden the sound with Blue Tack. If you're using the IClick it shouldn't make any difference, as it's a soft click and doesn't upset/hurt the dog when clicked close to the head/ears.
Also AFTER you've clicked don't give him the treat immediately, make him wait a second or two. He may mug you (Leaf still does mug me at times if she gets very excited) but he'll quickly learn "Hey I gotta be patience for that treat, Mom's not going to give it to me immediately".
Plus, I know when you want to praise him a lot, but keep it low key, he may be a dog who is distracted by excited praise. Just a quiet Good Boy, You're A Clever Man but not the full on PARTEEE praise may also help.
I recall you saying you cannot find a treat low enough. LOL I have the same thing here, Leaf is sooooooooooooo food orientated I tried, just as an experiment (don't recommend it as a full on treat) dry, stale bread and she STILL went for it as if she's never had a square meal or a treat before. So don't worry if you cannot find a lower value treat, some dogs FOOD ANY FOOD is a treat
All dogs respond differently, it's a matter of experimenting and finding what works best with your dog. And it can vary from trick to trick too. LOL they like to keep us on our toes! Just keep on keeping on, then he'll knock you flat (not literally I hope) by limping away as if he's being doing it all his life.
My boy Zeus can take a while, or rather could he's retired from tricking now, to learn a trick. He's the slow, methodical type of dog but once he's got that trick he NEVER needs a refresher course as he's got an elephantine memory. Whereas at times the quick learners need a refresher course. Brody may be a slower learner, number of reasons, but it doesn't mean he won't get it, just needs time.
at work and have not had a chance to work much on the limp yet so more time would be great for me and I might just manage to get something posted...! 
Loving seeing your guys progress though.
You're so right, now she has that first unaided step she'll keep building on that, as did Leaf once she took her first step she 'got it' and now will do quite a few steps without dropping her paw. We're now working on duration
. Hopefully Brody's moment will soon come