Just an idea, so no one is alone... I don't know how many rats you have, but this just kind of popped into my head. If you housed 3 rats per tub, and kept an extra tub empty:

Say you have A, B & C Females. and M Male.

A B & C are in their tub together.
Take B & C and put them in the empty tub.
Cycle in M.
Cycle out M.
Put B & C back in tub with A.

If you only have one male, it would work, but if you had two males cycling then you'd have to get a little more crafty to keep track of things and two extra tubs rather than one. This way, also, with the 3 females- you wouldn't have the scent of a strange female if, in case, you put female B into a tub with females A doesn't know. The smell of completely strange females could stress the pregnant female and cause her to abort.