Wait for an update from T-Mobile, Doesn't look like any cooks are posting information on how to extract the radio.
Search XDA for Dag's NBimagetool, search nbImageTool and you will find it.
Create new folder in c:\ drive call it NBImageTool or whatever you like.
Extract nbImageTool.exe to new folder
Extract Stock ROM to same folder
Open Command Prompt and CD to new folder
At commond prompt type
nbImageTool.exe RUU_signed.nbh
In folder you will see a file called radio.nb
Search and find HTC ROM TOOL RHODIUM
Extract anywhere you like
Copy radio.nb to same folder as HTC ROM TOOL RHODIUM
Run htcrt.exe
Go to ROM Builder tab and select Rhodium for device
Select new Radio.nb file for Radio
Prease create
Viola...your new Radio.nbh is ready to flash as you would ROM, use same customRUU to flash.
I know it sucks when people don't share knowledge...
EDIT
Use nbhextract.exe instead of NBImagetool.exe for now, nbhextract can be found with HTC ROM TOOL.
Small bug with nbimagetool that is being worked on now.