I think Kenny is saying to base the segmentation on a custom field and maintain the dynamic value of that custom field with a recurring campaign of its own. I've got that setup now and it should work out just fine.
I do still have a problem with how this is handled / enforced within the app, itself. Basically you are saying, "yes, we know it doesn't really work well to base segmentation on date values in a manner in which those values might dynamically change, even though we let you setup Smart Lists for Segments in just such a manner." I would think that you should, at the very least, throw up some alert text warning people when choosing dates for segments, especially when further defining date range filters, something to the effect of "Warning: Segmentation with Date Values may not work as expected. Unless the date aspect of this segment is static (e.g. related to Birthdates or Anniversary Dates), you may need to setup some extra plumbing to get the functionality you seek." Possibly even with a link to a help article.
I LOVE how much programmability and flexibility is provided in the app, giving us a ton of freedom... at least until that results in giving us enough rope to hang ourselves. Thankfully I caught this in sending some test emails to our Test Clinic and noticed abnormalities before launching it to real customers.
Much appreciated,
John