I got some very helpful advice a while back in this thread, most of which I've followed! About half of my recoveries are solo.
If there is no one around I will pull the boat onto the trailer with the bow line, and accept that I might get my feet wet (usually can balance on the trailer OK). If there is cross wind, or an onshore wind I'll wait until there is a passer by that will help with a control line.
There are some gadgets around that will "clip" the D ring to the winch post, but you need to drive the boat up all the way and I've never wanted to so this.
The problem with reaching down to the winch hitch is that you have to lean over the bow, and if the boat is not fully on the tailer, it tilts the bow up so it is higher still. I've done it but it felt like I could fall off.
I've been thinking of rigging up a long piece of PCV conduit with clips. (Could use an old fishing rod, or anything with a bit of flex, or maybe an angled join)The conduit would run from the tow bar, supported by the winch post or winch and droop down over the mid trailer. Before recovering, you would attach a rope to the clips - that will make the condiut droop to a reachable height. You then drive the boat onto the trailer, run up the front, grab the rope, pulling it off the clips, secure the boat, turn off the engine and winch up at your lesiure.
Sounds like it would work, but I've not tried it yet!
The other thing you could do is attach some steps / rungs to the hitch post to make it easier to clamber down.