End slow listings import & request rest using the missing Item ID's?

Hi there everyone. I've been importing my listings (55,000) into Sixbit for a week. It's done 45,000 upto now but the rate of import is down to about 100 an hour, so the remaining 11,000 will take another 4-5 days (at this rate). Is it possible to end the import and then ask the system to import just the missing Item ID's and not have to do all 55,000 again?

Many thanks in advance
Mike