Monaco Editor - How to make some areas readonly

I'm trying to configure the Monaco Editor in a way that certain regions of the textcontent are readonly. More precise, I want the first and last line to be readonly. Example below:

public something(someArgument) { // This is readonly
// This is where the user can put his code
// more user code...
} // readonly again

I already did something similar with the Ace Editor but I can't figure out a way to do this with Monaco. There is a ModelContentChangedEvent that you can register a listener on but it's fired after the change happened (so too late to prevent anything). Does someone with more experience with Monaco got a idea how to do this?

Thanks in advance!

from Monaco Editor - How to make some areas readonly