I like to have tools that are a comfortable blend of both specific and diverse, simultaneously. And trailer applications are one of those tools.
I'd suggest one of two simple solutions, the first being what could easily be the simplest of those: if the trailer deck is flat, then cut it to create a beaver-tail. As I was building my utility trailer, I thought all that I'd ever haul on it would be dirt-bikes, ATVs, and mowers. But it occurred to me that I may need to haul my Harley (or at least someone's) on it occasionally. So, I went about 16" forward of the tail, and v-notched the frame and dropped the rear down about 4". Cut some fillers, and welded them in. Made a huge difference in what I could load on the deck. It made the ramp hinges about 4" closer to the ground, and made the transition from the ground, to the horizontal surface of the trailer, much more gradual and user-friendly.
The second suggestion is: the same as Nor'Easter suggested - a split-folding ramp. Almost as easy as my first suggestion, but you'll have to buy some material and weld it up. I think a good starting point/formula would be the 50% rule. I would think that if your current ramp is 5' long, then the added segment would suffice if it was 2.5' long. Or if your ramp is 4', then the added segment should be 2'... you get the idea. But you'd have to do some math to determine what angle and length would work best. Remember though, any added material will add stress to the mounting points, the ability for one person to safely raise/lower the ramp, etc.
This would make a fun, little Saturday project. Post up some pics once you get it done.