different MTU on different VLAN's

I want my regular eth0 interface to have an MTU of 1500, and have eth0.12 with an MTU of 9000, but Linux seems to want to keep the MTU consistent across all VLAN interfaces. Has anyone done this before? I don't know if it's a limitation of my Ethernet hardware or of Linux. In theory, as long as Linux only transmits <=1500 byte packets it shouldn't matter what the underlying hardware is set to, so I don't know why this restriction exists. Thanks James