Sorting the stats by "last week" (if that's what you meant) will only show the player's totals for the previous 7 days. However, it won't show you which stats were accumulated while in the active lineup (and therefore counted towards the team total) and which stats were earnt on the bench (and therefore didn't count). Therefore, unless you are playing with weekly lineups, this probably won't give you the results you're looking for.
My first thought was that at the end of each week you could save the league stats and get a couple of people to verify that the results are correct. Then, you could subtract the previous week's season-to-date totals from new season-to-date totals to find out each team's stats for the week. You could then manually calculate the roto points based solely off that week's stats. It's a little complicated, and ERA and WHIP might be tough to calculate, but I could see it working. Good luck, it's certainly an interesting idea.