I did all my transactions by computer. just go to groupme.com and click login, then click on register. once registered, go back to split.groupme.com and log in and create split.
make it 499 per person and the click create link. use incognito to follow that link, and then chip in without logging in. you can do that as many time as you wish... (I think.. I just did it with two "people" each time)