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<shrug>
Send a feature suggestion to the support address. The more official interest they get the more likely they are to add a feature.
Script Debugger has does auto-pairing, and one of the things I like about it is that it will enclose the-selection with brackets, braces, or parentheses in addition to doing a simple pairing.
Luca's suggestion will do the same, although you have to remember your keyboard shortcuts.
Another possibility is AppleScript with which you can get quite fancy if you're so inclined.
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Best Regards,
Chris