Lowered Prius - rear helper spring

Recently installed H&R lowering springs along with new KYB struts on my Gen 2 Prius. The front fits like a champ but when the vehicle is lifted off the ground for maintenance and the suspension is fully extended, the rear springs are not long enough to hold hold firm on the perch and they move around, which requires me to reseat them prior to lowering the car back to the ground. It looks like this may be a pretty common situation and it wouldnt take more than 1" to resove it. I'd like to eliminate this problem and a possible resolution appears to install a helper spring, although I don't know if this will work on a strut. Has anyone had the same experience or have any suggestions on how to resolve this?

I'm considering the Eibach 2.5 helper spring and coupling spacer. Can be seen on Summit Racing.

Thanks!

 

I installed the front and had the dealer install the rear, but they never mentioned the extra play in the springs. I finally realized it was an issue around 6-months later when one shifted enough to started making rear-end noises out of the driveway and around corners. California roads are so bad that after several hard bumps one had shifted out of place. The dealer then made me aware when I contacted them as they read through the mechanic's notes. Better to know later than never. They said they would install a solution at no cost if I found one. The only solution they suggested was go back to factory, which isn't going to happen.

If at the point where the spring meet the lower perch is 2.5" inner diameter then I think the Eibach helper spring and spacer would work to hold it all together, although I think it's technically made for a coil-over. But would adding them defeat the purpose of the lowering springs?

 

I'd post a link but I've been a lurker for too long. Don't have rights too.
Google Summit Racing HELPER250

 

Thanks for the feedback guys. H&R was less than helpful so I'll get in touch with ground control. I wish I would have heard of these guys before then.