I've seen the curb rein thru a martingale, but I have never done it. If you can get your horse to bend gently left to right, you can "take and release" gently left to right ("climb the ladder" as one old timer put it) to collect while squeezing a little.
If the horse were mine, I get someone to air the horse up from the ground with a plastic bag or a little baby powder or whatever and see if the horse will raise up. If you "keep riding" while the horse is aired up, you get a pretty good feel for where the horse can go and the horse gets the feel too.
I also like to work in lines or a jog cart. Turning the horse loose with side reins and chasing him a little tells me where the horse can comfortably put his head.
I think trying a pelham or a pelham thru a martingale sounds too much like the rider trying to make a horse put his head somewhere rather than letting him, or at most, asking him.
I sound like a broken record, but collection comes from natural conformation and bending the horse left to right with his head lower but back against his neck. This lets the neck come UP and out of the whithers, hinges appear, and then when you want the show ring head set, you just air the horse up and his head will be a nice place and he will keep it there and use his ears.
If you decide to try this, do it about three or four times and then the next time "call on the horse" to set up where you want him and see what happens. I think you will see some progress. All done in a snaffle bit.
Keep it simple, stick to the basics, and less is more.
JMO, of course.