Ouch, 20 to 30 minutes between target changes? I suppose if you're doing precision bench shooting... but for handgun? Obviously patching your targets every 3 minutes or so is completely out of the question then...
If you come at a time where your outdoor range isn't so crowded, there are tons of stationary drills you can do: Bill Drills, El Prez, draw-shoot-shoot from surrender and relaxed positions, prep-aim-reload-shoot-shoot, draw-shoot-shoot-reload-shoot-shoot, etc.
But it depends on what you want to accomplish. You can work on accuracy of course and trigger prep while stationary at any range. Sadly in your case, even simple target transition drills are obviously not in the cards. You'll need another range for that. Plus ideally you want to use a timer, and practice with others while taking turns playing RO. Where do the other folks who do USPSA in your area practice? Since you're American, can't you guys just find the nearest abandoned sand or rock quarry and go wild, or have I watched too many movies?
While you can practice a number of stationary exercises, you can also do tons of movement exercises at home doing dry fire drills, including drills to help with target transition and quick sight acquisition (without even firing!). You can also practice reloading and firing on the move. Get a small length of 2x4 as a fault line, and set it even with outside wall corners or a door opening for barricade practice. Take a bar stool and practice getting in position to shoot under it between the legs at some small dot low on a wall. Use your imagination here... if you do this everyday at home, and combine it with weekly stationary shooting, you'll quickly improve depending on your current shooting level even if you don't have an ideal range to practice at.