Using a custom event action to trigger a Filemaker script

Hi,
I want to use a custom event action to trigger a Filemaker script. I know I can do this using the FMP protocol but I need to be able to get the value for the field BEFORE it gets changed as well as its CURRENT value. How can I do this? Even if I use the "Before Event Save" action the record seems to get updated before I can get its previous value.
I want to use a custom event action to trigger a Filemaker script. I know I can do this using the FMP protocol but I need to be able to get the value for the field BEFORE it gets changed as well as its CURRENT value. How can I do this? Even if I use the "Before Event Save" action the record seems to get updated before I can get its previous value.