Yep, the first thing my breeder told me about training in preparation for show was to not teach sit until MUCH later, like after all other training and after they had plenty of experience in the show ring and know to stand. We still aren't doing sit because we are showing. I have always found teaching sit to be easy and stand nearly impossible, and I think it was because we teach sit so young and so ingrain it into them. I have found I really don't miss the sit command so far because they know stand (I actually say "look pretty" instead) and they stand like little statues perfectly mannered waiting for a treat. It helps with grooming, too. Lizzie is a bit shy and wants to sit when on the table being examined by the judge, so I definitely won't be teaching sit to her for a while. THey also know down, stay, wait, drop it, leave it alone, and recognize a bunch of other words like walk and leash and ride and cookie, etc. They even know time for bed and snuggle...but I am sure all of your cavvies have their own list of vocabulary that they respond to!
On sit, however, it is so easy to teach just by holding a treat or jingly set of keys back far enough over the pups head that he has to sit to look up at it. Say sit, treat and they usually pick up that command within the first session. If you also teach them to hold the position until you release them with the command "okay" it helps a LOT with keeping their bottom on the ground longer than 2 seconds. You just have to be careful early on to release them with okay before they start to move on their own.