Interesting...if you can get $600+ for a calf less than 2 weeks old, you could probably do it profitably.
I wouldn't be interested in selling my heifer calves, but if you want to, then go for it. Here's an idea, pen two cows in a small pen, one cow with a bull calf, one cow with a heifer you want to sell. Try to have both calves similar ages, but at least one must be newborn. Pull the heifer calf after she's 3 days old, put her on a bottle and out of sound of momma. There's a good chance the mother of the heifer will allow the other calf to nurse, at least that's been our (unintended) experience when we pen two mothers in close quarters with their babies.
The bull calves will wean off with extra weight, and mommas which had their babies removed shouldn't have any udder problems.
An alternative would be to just pull the calf at 3 days and let the cow get bred back ASAP. That will get you calving year 'round but give you calves to market as bottle babies all year. Most beef cows that lose their baby at 3 days will be cycling much quicker than if the calf was on them. You'd probably have close to a 10 month calving interval on the cows that you sold the calf and let the cow go dry.