Sort of like this. The LLLLL bit is the L bracket. Make sure its rated to handle something as heavy as a 2921 hanging off it though!
Code:
 |
 | L
W| L
A| L __________
L| LLLLLLLLLLLL
L|   +        +
 |   +        +
 |   + ROUTER +
 |   +        +
 |   +        +
 |   +        +