Step 1: find the datasheet for the PL2303. Not hard. It did occur to me that this is probably a counterfeit PL2303, because it was so ridiculously cheap, and it was possible that it didn't have a real DTR line. (Fortunately, it does.) Pray that it's one of the corner pins and not somewhere in the middle. Find out that it's the second one in on the bottom row, and at least be thankful that it's on the outside edge.
Step 2: grab the crappy office tools. Stare at them sideways a little, in disbelief that you're going to be able to solder something on to those tiny pins without irrevocably damaging the rest of the circuit. Remind yourself that you've done it before.
Step 3: cut away the protective coating. Remind yourself to bring in some heat shrink tubing this size to replace it later, knowing that you'll forget dozens of times before you remember.
Step 4: find a piece of wire, and try soldering it on to the appropriate pin. Carefully. Slowly. Easy does it... and... DAMN you just soldered the two edge pins together.
Step 5: find some stranded wire and use it as a wick to undo your accidental solder bridge. Realize the strands are smaller than the wire you were trying to use before (duh) and one of them would be much better; pull the strands out of the insulation, take one strand away from the others, thread it back through the insulation and you're ready to try again.
Step 6: solder it on. For real this time. Pat yourself on the back for getting this awful butane soldering iron to do the right thing. Realize you love this crappy soldering iron despite its general problems. Think fondly of the days when Radio Shack carried amateur radio magazines, had cross references for transistor replacement, and stocked whole aisles with resistors. (Sigh a little.)
Step 7: Carefully touch the other end of the wire to the DTR terminal, because you pulled out the female pin from your makeshift adapter (because there wasn't any DTR, so why would you have the pin in there anyway? D'oh!).
Step 8: remember what failure looks like. avrdude complains that it's unable to sync, repeatedly, and you never get past the "Uploading" bit. Or you eventually do see something about a failed upload, if you're more patient than I am.
Step 9: hit that upload button and look for success!
I suppose there should be some sort of "Step 10: clean up" or "Step 10: put it in a housing" or "Step 10: put back the damn pin that you pulled out so that you can solder this new wire back on to it". But there isn't, because I don't need it just yet. I'll wait until next time this becomes a huge problem for me, and I have to re-do all this work again. :)