I tried this today, and it does not work. As soon as you're the last member in the party, regardless of whether or not you are inside the instance, you get the "Your group has been disbanded." message and you can no longer que for more members.
And you keep somehow glossing over the fact that it's a 3 second lockout on a 45s cooldown. How often is pushing a potential cast or two per boss (assuming you somehow don't overlap interrupts with someone else) back a couple seconds going to make the difference between a kill or a wipe in a 5-man? Probably about as often as whatever small dps increase you get from improved mindblast, in fact it's probably less likely with the plethora of interrupts now. And if you happen silence a spell someone else would have kicked/shield bashed/etc. you're actually increasing cast frequency by shortening the lockout.
XI Wiki


