You certainly could do it by leaving them in the car, but then you'd have to mask the hell out of everything like this (especially when using a metallic paint):
Haven't seen step by step instructions, but if you have a Bentley manual, imagine you'd just follow the steps to remove the conv top and then the roll bar. Gundo over on PPBB did exactly that and it looks really nice. He said it took about 10 hrs effort.
Here's a link to the thread:
http://www.ppbb.com/boards/ppbbphp/showflat.php?Cat=&Board=ARCHIVES&Number=1074156&page=&view=&sb=&o=&fpart=all&vc=1
I'm happy w/ mine black - good luck!