Here's a workaround that works with Sketchup: in a separate terminal, I run:
$ watch -n 0.3 xrefresh -geometry 1x1+500+500
That uses xrefresh to create a 1x1 pixel x11 window at 500,500 on the screen every 0.3 seconds. That's enough to get sketchup to redraw itself.
If that's not enough, you can run xrefresh without the -geometry option to have it draw a window the size of the entire screen. But that's a lot more distracting.