Total Home DVR

The main DVR is wired to the gateway but you can have WIRELESS receivers that access the DVR.

I would like to set the DVR STB in a location where there is no Ethernet cable. is there some kind of dongle or accessory that will hook up to the USB port on the STB?

No!  But you could pay att the $99 to relocate the wall/street connection if desired.

Or pay $49 and a $10 a month fee to get a wireless stb. 

Yes, you could do that if you want to waste the extra $10/month with the dvr sitting by itself in the other room.  Plus @skeeterintexas already suggested that in post 2.