I have asked my Japanese friends about this and they are usually convinced after discussion that "ga" is the correct particle to use here. But "wo" sounds fine.

I think it is very much like "was/were" in English. "If I was to give you a cookie..." / "If I were to give you a cookie..." "were" is "correct" (as though there is such a thing in English), I think, but "was" sounds fine. "Was" looks pretty abrasive in writing but say it out loud and you'll notice that you hear it a lot.