Part cause of the micro-USB fiasco is that, funnily enough, you can't do that. Or at least not if you want OTG mode too.

It's all laid out in this PDF from the USB consortium.

Quote:
3.1.1 OTG devices
An OTG device is required to have one, and only one USB connector[...]
/Quote

So, if you have a functioning OTG-capable USB port you're not allowed to add a second one (for e.g. charging).

It's better to just get rid of the micro-USB charging mode altogether, it was a stupid idea to start with. Particularly as Nokia was one of the few vendors that used to have a functioning charging plug (unlike S-E and most other phone / PDA vendors out there).