Ah yes, I remember doing that while comedy off-roading as a child. (We weren't allowed outside unsupervised, so it was back garden cyclocross or nothing.)
I think if you want them to work properly, and give consistent tricycle handling, they'd need suspension. An un-suspended 4-wheeled vehicle being a 3-wheeled vehicle under all but ideal road conditions.
If it's just to stop the bike falling over as you mount and dismount, that's less important. I suppose tilting trikes are the preferred solution for this sort of thing, but I wonder if you could design something like streamliner landing gear that was lightweight and didn't require skill to operate?