When can a space shuttle make a SRB separation?

I've been trying to find out if the space shuttle can make a SRB separation prior to its normal time in the event of an emergency. Wikipedia lists the abort modes, but also says "No abort options exist from the ignition of the SRBs until their burnout 123 seconds... show more I've been trying to find out if the space shuttle can make a SRB separation prior to its normal time in the event of an emergency. Wikipedia lists the abort modes, but also says "No abort options exist from the ignition of the SRBs until their burnout 123 seconds later."
http://en.wikipedia.org/wiki/Space_Shutt...

The reference it gives doesn't make any mention of that however and I can only find information of HOW it separates, not if it can before burnout. I would think that it could but I can't find anything that says so definitively.
Update: @Jerry Lee - SRB's can be destroyed from the ground in the event of that.
Update 2: Ranged safety system refers to destroying the SRB's in the event that they go off course. It doesn't say anything about if they have a procedure for separating the SRBs and ET to allow the shuttle to return sately before SRB burnout.
Update 3: @TSW - I'm pretty sure the shuttle has engines.
Update 4: @Katie - If for example they knew in advance that Challenger would need to jettison the rockets, Shuttle safety really becomes a moot point.
However I did find this article which says why it can't be done.

http://www.space-shuttle.com/challenger2...
Update 5: @Ottawa Mike For a situation like Challenger. If they had a way to detect a SRB failure and felt the need to land earlier. All theoretical really. I see that they knew about the SRB and designed them to just be "fail proof" as the concern seems to be mainly about the shuttle engines failing.
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