Another approach besides escaping the curly braces would be to upload the script to the BigFix server and then use the download actionscript command to retrieve it. Uploading the script can be easily done with the REST Api and a tool like Postman.
This method works best if the script will not need to be changed on a regular basis though. It also makes reviewing the content of the script more difficult but certainly solves the problem of escaping braces. A similar problem exists with PowerShell scripts.
Have you thought about just using the sh type instead of action script?