Since the alt events are basically there for those who don't qualify for the main event of that week, my assumption is that you'd basically have to intentionally tank and not qualify for any of those bigger events.
I wonder if simming through your current season and then just skipping straight ahead to the first alt event would let you get in to it...I forget what each signature event's requirements are, but I seem to recall they are based on OWGR standings, FedExCup standings, or wins/results in other tournaments. By skipping a bunch of events, you'd fall in the standings and rankings and have no wins or high finishes.
Otherwise, I guess you could just start a new career and again just sim to the alt events, so you don't qualify for the bigger ones.
I think the next issue would be actually winning the alt events, because when you do, you'd likely earn qualification into the bigger events and have to sim thru seasons again to fall in the rankings and lose the qualification for winning in that season.