Is there an option to add this function with a script or something? This would improve my daily work a lot!
I'm sure it can be scripted
Check out the scripting forum
If you are using OSX try this AppleScript:
The zip archive has a script for setting the bleeds on the active page and one for the entire document. Save a copy of your files before running the script in case the results are unexpected. I haven't found any problems but my docs tend to be fairly simple.
Page items that are within .1" of the trim will get .125" bleeds. An image's frame gets bled so the image will bleed if there's enough overflow. Text frames get an extra .125" inset so that when they bleed the text doesn't move. Watchout for polygons, elipses, or irregular shapes touching the trim.