If you wrote the bill, I have no doubt that it would look like a OSS-proponency bill.
No matter who wrote it, it would appear so to you. Mine would simply say that the government must buy the lowest-cost software available that fits objectively written criteria for the task at hand. Then I would have RFPs and purchase orders reviewed for being targeted, and reject them if they were.
That goes both ways. If someone were targeting an RFP towards a Linux system and somehow the Microsoft bid came in lower (without using their slush fund), then Microsoft would have to get the contract.