Hello Glen,
you can configure a channel group made of N 64 kbps channels under controller t1 x/y config mode.
This creates a logical serial interface and you can configure it for FR encapsulation.
Actually you can associated all the B channels to the logical interface and then the BW parameter can be associated by the FR WAN provider to the logical virtual circuit this is the common way to perform this.
I've found an example of configuration: actually this module provides you directly a serial interface and controller t1 commands are given in interface configuration mode
http://www.cisco.com/en/US/docs/ios/interface/configuration/guide/ir_dsu_rtrs.html#wp1032260
But the principles are the same I've described above.
Hope to help
Giuseppe