As far as I know there is currently no drop-in replacement for the rrdtool write plugin. That being said, there are a number of other write plugins which can achieve your requirement. Have a look at the table of plugins on the collectd wiki. I'm thinking about carbon, graphite, mongodb or likewise which are based upon some sort of database backend, which can most likely be set up to be trimmed periodically, thus preventing the endless growth of used disk space.
Moreover, if you are patient, the 1.5 branch of rrdtool should implement an architecture independent format (version 0005), you might checkout github to find hints on whether this is being worked on right now, or else ask Tobias Oetiker for a roadmap.