Thank you for your suggestion. I tested it and it adds 1 additional collision check per tick for every solid in the level. Not too shabby.
But in the meantime I have found another solution which adds no additional collision checks per solid.
When the player collides with a solid, a helper object is created at the same position of the solid, but with two differences: It is a little bigger than the solid and it does not have solid behaviour so that the player can overlap with it. So now you only have to check one single object for overlapping with the player. If the helper object overlaps with the player, the solid "kind of overlaps" with the player, too. If the helper object suddenly doesn't overlap with the player anymore, neither does the solid. In that case, the helper object is destroyed and the text is changed to "not on collision".
Now of course it's gonna get a little tricky when you have different types of solids with different forms and sizes but maybe rexrainbow's nickname plugin can be of help then. If I decide to investigate that matter further, I will check back to this thread.
https://www.dropbox.com/s/noyf149ldkgr5 ... .capx?dl=0