Fortigate 100D USB Modems

The Fortigate 100D has 2 usb ports in front. Do you know if the 100D can support (2) USB modems at the same time via load balance or fail-over?  I have a site that does not have any copper internet, but i was thinking of adding a USB Verizon and a USB ATT and have them load balance.

I know i can get 1 to work, but haven't tried the second one.  Just wondering if anyone has done this.

-steve