Force a VLAN interface up on an MSFC

[jdavis1]

I have a situation where I am replacing the network hardware on a campus. In conjunction with the hardware replacement, the VLAN structure is also changing. What I am doing is using a Cat6500 (CatOS 8.1) with MSFC2 to bridge the old and new network together. The old network has a Cat5500 at a core and a 7206VXR doing inter-vlan routing. I have trunked all the vlans on the 5500 over to the 6500. On the MSFC, i have configured VLAN interfaces for all of the old VLANs as well as the new VLANs. Where an old VLAN corresponds directly to a new VLAN, I have bridged them together. The idea is to move the routing off of the 7206 and onto the MSFC, then keep both the old VLAN running while having the new one available to migrate users to. So it looks something like this

! Old Vlan definition on MSFC:
interface Vlan18
description *** OLD vlan
no ip address
bridge-group 3

interface Vlan31
description *** NEW vlan
ip address 10.1.1.1 255.255.255.0
ip helper-address 10.1.2.1

This seems to work okay, except that the NEW VLAN is inactive until an active L2 port is present in that VLAN. Does anyone know how to force a VLAN interface active even if there are no active L2 ports in that VLAN?