I am currently considering how to do this, I have the same problem - a short-door car with the old flappy sidescreens. It's so annoying that I run without sidescreens whenever possible
One option is to fit the Librands sidescreen steadies, which are reputed to work very well, but I'm a bit concerned about intrusion on arm space. I've got a set, but not fitted them yet as it requires drilling the the doors, so it's a one-time thing if you don't want to end up with holes in the leather.
Another option may be to fit the new windscreen rubbers, but to get the old-style sidescreens to fit into them the sidescreen rubbers would need to be cut back to about half their existing width so the rubber is thick enough (and therefore stiff enough) to move over the lip of the windscreen rubber rather than sticking on the outside of it.
