Probably won't be possible with a cat but on Vee bottoms it's pretty easy.
I have taken many a boat off a trailer by just using poppet stands and keel blocks. You need two short boat stands, one for each corner of the stern and numerous pieces of sturdy blocking (cinder blocks with wood caps also work well).
Get your trailer in position, put a stand under each corner of the stern and then screw up the stands so the weight just comes off the back of the trailer and then maybe 2 inches more. Keep in mind that poppet stands are not designed for holding a boats weight so you need to do everything in baby steps (in 2" increments depending on your blocking thickness). Ensure the weight of the boat is on the keel block not the stands when you are done aft.
The key to blocking is having the weight off the trailer, and on the block with just a little weight load on the stands for transverse stability.
Slowly pull out the trailer just until you are clear to block the bow. Trust me the boat will sit there just fine.
Depending on trailer configuration and height you may have to jack the bow higher once the trailer is removed by using a large hydraullic jack with a wood cap to spread the load and add some blocks under the bow. Only go 2" at a time and block as you jack. When you are done the boat will look just like they do in a marina for winter storage.
I have never done this on a bunk trailer as I owned a big roller trailer at the time but it would work in a similar fashion as long as your bunk coverings were in good shape. Our trailer had a big center roller aft that carried the bow pretty high as the boat neared coming off the trailer. It's really not as scary as it sounds.