Check this out hxxp://unmrkd.net/heavenlymodz/uncategorized/create-another-nand-image-with-a-different-keyvault-to-prevent-banning-on-xbox-live/
The guy used a known BANNED keyvault and mac address to create his hacked NAND image and put it on the Cygnos. This ensures that if someone accidently tries to go on Live while using the dirty NAND Live wont ban the clean NAND. In essence Live (hopefully) thinks that the two NANDs are two different Xboxs. Sweet simple clever mod. Why didnt I think of it? its so obvious!
i somehow doubt there are tools available to do that with a slim however.
What you meaan dual NAND board/chip? There are already right ups to wire a cygnos on a slim and I'm sure once the add on parts are available, there will be tutorials to do it with the progskeet. Plus once there is some more confidence in the dual boot method (no bannings) Im sure there will be many external/addon NAND board vendors.