Just to completely answer the original question, no, you can't use the Wii U's sensor bar. After the big spring update the system no longer powers the bar unless a Wii remote is active.
I've been using a USB powered bar from Nextronics and I hate it. The LEDs aren't consistent, there aren't as many of them as the Nintendo bar has, and it can't be read by the remote from any angle. It has to be placed below the TV, level with the remote, in order to work. It's a piece of shit.
You can see the difference here: http://ecx.images-amazon.com/images/I/41Uqw8UsCPL.jpg
I'd recommend trying a wireless bar instead- good rechargeable AAs are cheap.
I've been using a USB powered bar from Nextronics and I hate it. The LEDs aren't consistent, there aren't as many of them as the Nintendo bar has, and it can't be read by the remote from any angle. It has to be placed below the TV, level with the remote, in order to work. It's a piece of shit.
You can see the difference here: http://ecx.images-amazon.com/images/I/41Uqw8UsCPL.jpg
I'd recommend trying a wireless bar instead- good rechargeable AAs are cheap.