it may be possible, however i certainly wouldn't want to dick with the ABS unit and it's associated wiring. it's something that could cause total brake failure if it goes wrong. atleast with the line locker fitted into the rear brake line, should it fail and lockout the rear brakes the front brakes will still work
Yes, there may be safety issues (and the scrutineers at the track may not like it because of that). I still think that it is worth considering for a dual purpose road/track car.
(Temporarily) disconnecting the harness connector at the ABS control module, meaning the solenoids aren't energised, results in the system behaving exactly as does a non-ABS system.
The appropriate solenoids (I think that the VR system is 4 channel, hence the plural) could then be energised using an external controller. Another harness connector cut from a wreck could be used to make the electrical connections.
It would be necessary to figure out which of the solenoids are those for the rear brakes. Doing that is trivial with access to a wiring diagram.
I am not sure what the signals to the solenoids look like. It may be that the ABS solenoid valve 'hold' function (which would isolate the brake caliper associated with it from the master cylinder) is achieved using a signal with a duty cycle. That would have to be measured and matched if that is the case.
Alternatively, the ABS 'dump' function might be used, which is more likey to be either 'on' or 'off', simplifying the control. That would also require the ABS pump motor to be powered though.
Wiring the set up in series with a front wheel speed sensor based frequency switch would allow it to be automatically turned off at anything greater than the slow roll required during the burnout. That is arguably safer than the conventional line lock in that respect (unless a similar switch is used for that too).