Get two 2 x 6 4-5 feet long. Split it them at a 2 - 3 degree angle along the thin edge. Leave at least a foot of untouched "flat" wood on one end. It wouldn't hurt to attach a larger block to the end of the flat section as a wheel stop so it can't roll off.As others have mentioned, I think it will be difficult. I have a slight incline on my driveway and I can't push my 3000+ lb pup up it at all. Our scout troop bought a trailer valet for the troop trailer which works for them, but I need to build a slight ramp to get over the lip into the hut where it is stored. The only way the valet will get the tires over it is with additional scout help, or loading up the nose of the trailer to increase the TW, preventing the valet tires from slipping.
I plan to try it on mine to see how it works.
Back the trailer tire all the way up to the lip edge where it won't go in any further. Put the split boards with the foot of "flat wood" in front of each wheel (opposite side to the lip) so it can then be rolled away from the lip, up the ramp on to the flat spot.
With the trailer now up off the ground on the 2 x 6 place the other half of the board back on it so its essentially a whole 2 x 6 (minus saw blade thickness).
Congratulations, you have not raised the trailer to the same height as the lip (assuming its a standard garage type lip) and you can not back it directly in with no additional assistance.
If your lip is higher than a 2 x 6 then get a bigger piece of wood and plane to the correct height and split it the same as I described (more height will mean a longer board will be needed however).