Limit amount of dynamic fields to a 1000

Hi all,
My use case is that I am indexing documents over which I have little control, and would like to use dynamic mappings. However, I would like to limit the number of fields in each index to a 1,000 (the default value). The problem is that for documents that cross this threshold, I would like to index only fields that already exist in the index, rather than drop the entire document with an illegal_argument_exception: Limit of total fields [1000] in index[...] has been exceeded (similar to what ignore_malformed does for fields with wrong datatype).
Is there an easy way to achieve this (a flag similar to ignore_malformed maybe)? My current idea is to disable dynamic mapping on an index once I hit this error once, was wondering if a better solution exists.

Thanks in advance!