No easy way I know of but the good news is that it doesn't have to be done very often. I position the spring/strut and grasping the end of the strut I compress the spring with the objective of pushing the strut back into the hole. I use a side cutting pliers for grasping the strut.
I cut a groove in one side of a pair of slip joint pliers, not channellock type, just the ordinary two position type mechanics pliers, and I think I cut a notch in the other end. I can hold the strut in the notched end and compress the spring with the grooved end. Works very well.
Brownell's sells a mainspring tool especially made to do this, however a friend at the club the other night said that he has used a small cocktail fork, the two pronged ones for eating shrimp, and that has worked well for him.