Issue "hook flash" from GVP

[gunnadl]

We have a Rockwell Spectrum sending calls to a Cisco media gateway via TDM to a GVP connect to the media gateway via IP.  When the GVP needs to perform a transfer to a rep, we are tying up 2 of the TDM channels and the call stays on the GVP for the duration.  Is there a way that the GVP can issue a "hook flash" versus a SIP refer in order to break the connection from the Spectrum to the GVP?  Our media gateway does not recognize the SIP refer.