A new version of SWF Investigator was released on Friday (version 0.6.2) and I will be updating the open-source repository in the next day or two. When the update is complete, I will respond to this thread so that you know to pull down the latest version of the source code.
For SVN access, I have used TortoiseSVN on Windows which is supported by SourceForge: http://sourceforge.net/apps/trac/sourceforge/wiki/TortoiseSVN%20instructions
The logic for your feature request already exists in SWF Investigator but it is currently commented out. For the next release, I can work on enabling it. If you want to play with the functionality in the meantime, then the code is in SWFInvestigator/src/decompiler/tools/Disassembler.as.Within that file there is a function called, "start." Within that function, there is an if-block which checks for "showOffset". You will need to uncomment the out.print() statement within the showOffset if-block. You will also want to set showOffset to true just before the if statement. Recompile the application and it will begin to show the information you want.
Fantastic, thank you! I'll look at the source code in a few days once you've updated these latest changes and I'm back from vacation...