After many trials and tribulations (and having to frog a section and a half), I am FINALLY finished with my Citron! This is the second Citron that I've blocked, since I also blocked Kirsten's, so I have a bit of extra wisdom as to the methodology for getting the desired results.
Now, triangle shawls require extremely aggressive blocking to stretch open the lace and pull sharp the points. Citron, however, is a very different beast, as she lacks both lacework and points. The pattern recommends threading blocking wires across the flat edge, which is critical to getting a good result, but that doesn't answer the question of how to treat the curved edge.
The quandry is two-fold: first, how to stretch the pattern without using a thousand pins, and second, to not over-stretch, which would make all that pretty rucheing look like nothing more than slightly darker stripes.
Kirsten wanted her shawl blocked rather aggressively, so stretch I did. I pinned it at the base of the ruffle, i.e. along that last increase line, and did not put any pins along the cast-off edge. The result was a pronounced ruffle and a wide shawl. Ruched sections do look a bit more like darker stripes, but the heavily variegated yarn she used minimizes this effect. Pinning at the base of the ruffle allowed me to use fewer pins, since the ruffle itself did a good job of hiding any hint of a point (I only had about 25 pins to use for hers, so it was pinned every 3-4 inches, which resulted in some gentle pointing). My only complaint with this method is that the resulting ruffle is very curly (this may be a feature that you desire, in which case this is the just-right method).
For my own Citron, I wanted the ruffle to lay as flat as possible, with some gentle curling just at the very edge. I had accidentally left it to soak for two days before I remembered to pull it out of the basin, so even a gentle stretch resulted in a rather aggressive blocking, since the fibers were so saturated. I pinned every inch or less along the cast-off edge, as well as every 4-5 inches at the base of the ruffle. This did an excellent job of flattening the ruffle -- so excellent that it no longer resembled a ruffle at all! I resolved this by un-pinning the entire shawl and re-dampening just the ruffle. I laid the shawl flat (no pins) and the next day the ruffle was PERFECT: mostly flat, but with a gentle curl at the cast-off edge. This solved the problem with the ruffle, but the rest of the shawl was still terribly over-stretched, and I was not especially pleased with the result. So I re-dampened the entire thing (I dipped it briefly in a basin of water, though a squirt bottle would probably have worked even better) and again laid it flat to dry without pins. FINALLY the shawl had the look I desired.
After all these experiments, my recommendation is this: Soak the shawl overnight, then either run it through the spin cycle on your washer or thoroughly squeeze out excess water. As the pattern states, run blocking wires across the top (flat) edge. I recommend NOT using ANY pins whatsoever. Instead, stretch and smooth it into shape with your hands, and then take a towel or an extra set of blocking mats, and lay them over the top of your shawl. The weight from the extra fabric will help to hold it in place without causing over-stretching. If you do want to stretch your Citron, then block it as I did my own: first, with several hundred pins, and then with no pins at all after a gentle re-dampening.