bsdlabel on root disk

Dear list,

Sorry, I know that this question arose several times, but I couldn't find 
anything useful via google and I never paid attention because I never thought 
I'd have that problem, but now I do:
How the heck can I manipulate the bsdlabel on the root disk?
The machine is some hundred miles away so I can't boot from CD to do that.
I have to write a new label to a running system!!!

Thanks,

-Harry