how to refit steel ring back onto drive shaft seal?

Hi, I changed the struts on my renault espace (1st one no bother, 2nd one bother....) i had trouble fitting hub back onto strut and resulted in the drive shaft coming out of gear box!! I have managed to put back the top part of shaft and refit seal but am having extreme difficulty in refitting the metal ring that goes back over the seal, is there a trick of the trade in how i can refit this whilst still attached to hub or do i have to remove from hub and do it off the car!!!