You could shim the threaded stud so it doesnt bottom out (I've done Fox III springs this way -otherwise the threaded rod hits the frame before the spring is compressed).
Otherwise, the LCA bolts are nice and loose, right? I have Prokit springs, which are pretty tall for aftermarket springs, and they pop right in.
The alternate method is to disconnect the LCA bolts and remove them. Then reattach the ball joint. Your LCA is now pivoting on the fulcrum created by the strut. Put a good, large floor jack under the LCA. Put the spring in place in the perch. Then jack the LCA up and install the LCA bolts. If you want to read about this, it's referred to as the MFE method here and on the Corral. It's how I've done springs on most cars since I was a kid. You have to be real careful with the jack (and have a good, big jack. No 15 dollar specials) but it allows tall springs to be reinstalled because the pivot point (BJ) is so far from the spring (whereas the LCA bolts are too close to the spring).
Good luck.