Been promising myself for ages to set aside a day to play around with the API, but I haven't as yet. You should be able to access the API by practically any means - bash, perl, php, C, windoze.exe, etc. From the looks of the Mail functions you could set up multiple forwards individually for one account and remove them as they become redundant. It doesn't appear to have a mail-add_account function (which would likely be abused - eg. mailinator.dreamhost.com) but it might allow you to add filters to forward to addresses outside your domain. Only thing I could suggest is to just dive in and start toying with it.
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How To Install PHP.INI / ionCube on DreamHost