I've got a form finally put together that I'm very pleased with and it works exactly like I'm wanting except that the total field isn't updating propertly in certain instances.
If someone registers a foursome for the golf tournament, they're charged $75/player = $300. If someone also decides to be a corporate level sponsor for $1000 they get a free foursome team to play in the tournament.
I added a single product item with a value of -$300 that appears if they've requested a foursome (so they can enter their player names) and selected to be a corporate sponsor. For a total of $1000. If I didn't add the discount, the total would calculate to $1300.
When you submit to PayPal, the items and totals are reflected accurately. It's only the total field on the form itself that doesn't recalculate properly given the different combinations and options available.
Foursome w/ Corporate Sponsorship Prices Correctly at $1000 Total
Foursome w/ Major Sponsorship Prices Incorrectly at $500 Total (should be $300 for the foursome + $500 sponsorship = $800 Total)