Well, anything can be hacksawed off, or with a bit of luck have the rivet hammered out. Trouble is that when you run separate shifters and brakes, they're meant to go on the bar in a certain sequence. And I think a brifter mount will get in the way of a separate brake mount, even if you've cut the lever off.
I never learned to ride a bike. It is my deepest shame.
I have removed a lot of shifters from shift-brake lever combos - the early Rapidfire shifters were less reliable and had to be replaecd more often - the shifter mount could be cut off with a hacksaw and a separate shifter 'pod' could be bolted into place beside the remaining brake lever.
However, the "E-Z Fire" shifters like you have are not like the old ones - a shifter mount on the side of a brake lever. I believe the 'body' of the brake lever is really the same as the 'body' of the shift lever. So you might be able to remove the lever but there is still half of a brake lever remaining and you will have trouble mounting a new lever so it does not interfere with the shifter.
Happily, you can probably get a set of separate rapidfire+ shift levers for $30 or so and they are designed to work with separate brake levers.
By the way... what is the problem with the brake levers? THe levers just don't feel good or is it an actual problem with brake performance?
yeah. these feel cheap (rest of the bike including shifters feel great). maybe i'm being picky. i guess i'll stick to these for now and when they break down i can look into sd7 levers ($25) and alivio 410 shifters ($35). before this i had a deore drive train (= awesome) but i am still pleased with these components. they work. never missed a shift going through muddy hills.