If you have the luxury of re-ingesting all of your data nightly, you could leverage an ingest design pattern like this (https://wikis.oracle.com/display/endecainformationdiscovery/Derived+Datetime-based+Attribution) to produce a "DaysAgo" attribute. From this point, you could then write your range filter syntax to pull records LT 90 days.
If you don't have this luxury, you could write a custom QueryFunction leveraging the EID product SDK. Check out Chapter 5 from the Studio Developer's Guide to learn more about leveraging the SDK to create your own variety of the RangeFilter QueryFunction. http://docs.oracle.com/cd/E29805_01/studio.230/StudioDevGuide.pdf
Thanks a lot for the suggestion. I ended up by implementing this requirement with Deep Link feature. This way I calculate in Java code the SYSDATE-90 and set the deep link dynamically. In my case, I have an OAF page that holds the Endeca, then I created a controller class that creates and set the deep link parameter in runtime.