[Zope] ZCTextIndex question

I have a ZCatalog that has grown to about 6.3Gb in size and as a result no longer fits in memory - resulting in a severe degradation in performance (a search that used to take less than 2 cpu seconds, now takes 5-14 cpu seconds). Is there any way to 'extract' a single index from the ZCatalog (a ZCTextIndex) and hold it in memory to improve search retrieval performance ? Also, because we are using the OkapiIndex relevance ranking process, we will need to hold the Lexicon in memory. Has anyone tried/accomplished this? Hoping there is a solution... Jonathan