BLF/Presence Watch (hint) a DISA()

Can a Hint() be setup and used to indicate to its subcriber when/if a DISA is being used?

dialplan examples greatly appreciated.

Phone set is a Grandstream 2020, with latest firmware (1.2.1.4, released June 2009).

Thanks,

asterisknow 1.5.0 (final)
yum updated to *-current as of this posting date (2009/6/22)