The only viable solution is to use an IQ table for this. There are other options, but they do make it more complex than it has to be.
It would be possible to have this data sitting in an ASE or ASA database somewhere, too, but increases the cost and complexity. I would look to IQ 16 and place the table in the IQ main store. This will give you much better performance (IQ16) than before due to architectural changes made to IQ in v16.
You could also keep the table in the catalog file (don't use a second catalog dbspace!), too. As you point out, though, when the catalog is synced the data is lost. To avoid this, a simple script could be written to copy the data back to the coordinator at certain minute/hour intervals.
Mark