DateTimeInput calendar start day

I am trying to change what day of week the DateTimeInput calendar popup starts with.
Here in Sweden we really like to start with Monday instead of Sunday.

I cant figure out how to do this.

A fellow countryman asked this question before. The answer is that the component doesn't support it but some magic can be applied and Victor supplied an answer that seemed to work.

Pascal just mentioned this in one of his posts yesterday:

It's far from perfect. Things tend to get out of place quickly.
For example, the previous/next month days used to fill the empty spaces are still there, so you get lines with only useless days AND empty spaces, and when it creates a new line the popup doesn't scale.
I'd rather keep Sunday-starting rows than mess the whole thing up.

I guess it's all fixable, but frankly it gets way too messy and complicated just for this.