I understand the following from your statement "All I want is
<$framefilename_no_ext>, but I can't save that option on the
Style Settings tab"
You need the topics to be generated with the filename without
extension. But at the same time, you don't want to change the Topic
Name Pattern Settings.
If I understand your requirement correctly, you can achieve
this in RoboHelp8 / TCS2.0. This can be done through Topic Name
Marker functionality. This functionality allows the user to split
the source document at any location where a FM marker is inserted
and the topic name is mentioned as marker text. RoboHelp picks up
the marker text to generate the topic name. Please let me know if
you need further elaboration on this or you can refer RH8
help.