It'd be easy enough to do, but do you definitely want to? A lot of places I've worked reuse activities if they fail testing.
On the assumption you definitely do, it would be easy enough - you'd want a postop trigger on mkbl and deliver. You'd want the trigger to find out what activities have been delivered/baselined, then run a cleartool lock -obsolete on them.
I'd have a look at "cleartool man mktrtype" to get you started.
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