Juniper supports this as of version 10.0 or newer (currently on JunOS 10.1). From the 10.0 release notes:
Multiple VLAN Registration Protocol (MVRP)
Protocol (MVRP) is used to manage dynamic VLAN registration in a LAN. MVRP
is an application protocol of the Multiple Registration Protocol (MRP) and is
defined in the IEEE 802.1ak standard. MRP and MVRP were designed by IEEE
to perform the same functions as Generic Attribute Registration Protocol (GARP)
and GARP VLAN Registration Protocol (GVRP) while overcoming some of the
limitations in GARP and GVRP, in particular limitations on bandwidth usage in
large networks with large numbers of VLANs.
—Multiple VLAN Registration