Here's a good thread from the Aquamist site about Meth, water injection and so on
http://www.aquamist.co.uk/vbulletin/showthread.php?t=1801
The flex option sounds good if you have the Syvecs installed. If you want to water injection your idea a of Direct port is still an option.
The flex sytem wasn't an option for me when | put my direct port sytem in.
When My car ran a Ethenol and petrol mix with direct port water, It ran superbly. really low egt's, no Det and 2 bar on road fuel. It was installed jan 2008 and is still going strong.
It's been adjusted for 100% petrol and that's my default setting for the car in summer.