GET followers ids API 1.0 to 1.1


I am currently working as a research assistant at University for collecting all the followers ids of US 2012 congressional candidates twitter accounts.
(that is 1000+ accounts)
Since they have a various number of followers for each candidates account, the total number of followers are about 24,000,000+
Since we had 360 rate limit call per hour for GET followers ids in API 1.0, it was possible to finish one cycle of run per a day.

However, in API 1.1, it was limited to have 15 calls per a window, that brings us 300,000 followers id per hour.
This gets us more than three days to collect one cycle of run
(here one cycle means, collecting followers ids of each congressional candidates, which is 1000+)

I would like to know if there is other way around to solve this issue, than paying for whitelist.
Thank you so much in advance.