Having a flow that listens for a record in NetSuite and pushes to lookup cache is a perfect idea for this. You could also make it a listener and batch flow so you can schedule syncs to it and rely on real-time updates to it.
Once you do that, you'd then need to perform the lookup to the lookup cache with a transformation 2.0 step on the export of your regular flow, or do a lookup step to the lookup cache where you then map the response to the results.
Since NetSuite doesn't currently support mapper 2.0, you can't use the lookup cache directly there in the mapper.