[TxMt] Extending all language grammars?

[Rob Shearer]

Textmate's ability to write a new grammar which includes an existing  
one is nice, but I'd like to do the opposite: make all existing  
grammars include an extension...

I frequently use "structured comments", such as comments beginning  
with "TODO:" to note bits of code that I've only stubbed out, or  
"OPT:" for optimization opportunities. I'd like to be able to syntax- 
highlight the most severe of these types of comments so that I always  
notice these things as I'm scanning through a file.

I could just extend the grammar for each programming language with a  
few new rules, but a much much better solution would be to add the  
rules everywhere, such that anything within a "comment" scope and  
which matched my rule got an additional "todo" scope.

Does Textmate already have a simple way to do this?

Is there a better approach to accomplish what I'm looking for?