Your approach won't work-- OP_ADD is limited to 4-byte operands.  Changing
that would require a "hard" blockchain split / entire-network-upgrade.

I wish to submit the following draft BIP for discussion and possible
> formal BIP review.
>
> https://en.bitcoin.it/wiki/BIP_M_of_2_DRAFT
>
> It is a proposed alternative to BIP 16 ("/P2SH/").
>
> Thank you,
> Ben Reeves
>

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Gavin Andresen