i had the same problem. the short hooks on the magna exhaust would not stay in the rubber hangers. i went and got a heavy duty zip tie and tied the rubber hangers together as tightly as possible. this helped in two ways.
1- the new exhaust sat crooked and the ziptie being so tight let me possition it anywhere i wanted and it hasnt moved since.
2- a buddy of mine was driving behind me and noticed that the exhaust was bouncing all over the place as i was driving. the ziptie kept it tight in place and now has absolutely no movement.

now for getting the metal hooks in the rubber hangers.. i had to bend the passenger side hook up to be able to fit the rubber hanger inside. be careful not to bend too far but just enough! also, the stock rubber hangers have an unnecessary amount of rubber "clogging up" the center which prevents you from putting the metal hook inside.. i simply cut and shaved it off with a wire cutter and a razor to make more room for the hook. the rest was pure muscle getting it to stretch that far.

i hope this helped!