If you can get your hands on some original boots, its a snap. Otherwise you may be able to sneak some wetsuit boots on, though that usually requires adding a dart (wedge) to the front of the boot to make it the same diameter (at the top) as the leg.
After that, make a smooth cut just above the current boot joint, carefuly fit & mark the boots, apply the wetsuit cement as per directions on the can, and finish off with some 3/4" or 1" tape.
I can check & see what Poseidon boots are going for when I get back to the shop, they're going to be more expensive than wetsuit boots but they may save some time & work.