Hi,
Custom Actions is the way to go! you'll love it.
Basically, Playmaker doesn't output anything, it's an engine that process your Fsm at runtime, there is not "compilation" or "publishing" involved, you design fsms in Unity, and when you press play, they are executed.
PlayMaker is done in c#, and the building blocks are "actions", you use them in states to create the logic and do things.
in your case, what will happen is that you will use PlayMaker and existing actions to do all the usual work, and when you want your own piece of code, then you would create a custom action and use that code within an action context.
To write custom actions, it's easy, simply open existing actions and study how they are working. you can also check the online help for more details.
https://hutonggames.fogbugz.com/default.asp?W166Bye,
Jean