Far as I know, top is the only way to get them in/out... Just like the other guys said. I did my Bilstein 5100's by myself. There was NO WAY that I was going to get them compressed to get the tower caps on. I sat and stared at it for a while, then realized that I could put the floor jack under the FRAME (one side at a time) and raise the truck while letting the axle droop (stay on the ground). Basically the same as using a frame lift... axle's droop. Once I did that, the shock tower caps rested on the mounts with the shock at full extension. Bolted them down to the mount, lowered the drivers side, tightened the shock bolts, then did the same thing for the passenger side.
Hope that makes sense. Lemme try one other explanation.
Steps for 1 side (drivers):
1: Remove 2 shock bolts
2. remove the 3 nuts that hold the shock tower cap on.
3. Remove shock tower cap and the shock
4. cut retaining band off new shock, drop shock in place.
5. start lower bolt in shock, snug up bolt.
6. Place retainer on shock, and rest the tower cap on it.
7. place floor jack under frame just behind front tire.
8. raise the jack until the shock tower cap is resting on the tower mount and the studs are sticking through the mount holes in the tower cap.
9. install and torque the nuts on the studs to hold the tower cap in place.
10. lower truck, center shock in mount, install and torque nut on the shock.
11. torque lower bolt.
12. Repeat for passenger side.
Sounds complex, but took all of an hour tops.
Good luck,
Andy