nas is only single threaded when processing AO profiles and preprocessing rules.
If you are looking to run a long running LUA script off an AO profile, you need to do something that causes a second instance to be run via the nas scheduler for instance. As an example, you have the AO do something quick like create a file with the necessary information in it. The have a scheduled job that periodically checks for these files, reads their contents, does whatever long running thing you needed was, and cleans up. the scheduled job(s) will run concurrently with the nas AO profiles.
The sequential-ness of the AO profiles isn't a limitation of the nas - it's a protection because it saves you from having to code a mutex function if you have two AO profiles affecting the same underlying data.
You could also consider nas replication to replicate these "long running" jobs to another nas where they'd be processed separate from the first nas that was handling your time critical items.
Or you could use the nas "post message" to post to a message queue and the logmon probe to read that queue and execute a script on match.
Lots of ways to skin this proverbial cat.
-Garin