Actually, I now have the majority of my stem plants held down with plant weights. I'm using it on L. aromatica, P. stellatus, A, reineckii, and Mayaca. If I'm not looking for more stems/dense growth, I just lift out the plant, snap off the bottom few inches, reattach the weight and sink it back down. If I want a few more stems, I'll snip it 3 or so inches from the bottom, attach a new weight and push it down where I want it. For the Mayaca, I bunch a handful of stems together. For some of the others, I can at times hold 2-3 stems down with a single, "spread-out" weight. I've been doing it this way for the last 9 or so months now, and I've lot it. You need to develop a bit of a touch with the plant weights so as not to crush the stem, but I didn't find it that challenging.
Clearly, many of the smaller stems wouldn't work well with this approach (think H. micranthemoides). But it does wonders for the 'standard' background/midground varieties.
So, there's my approach to handling stems!