Modifying the run configuration before execution

Basically, I want to modify the environment variables of the run configuration when a user clicks on the debug button, but I can't seem to find an interface/class that I could implement through an extension point which would let me do that. Seems like in the older APIs there was an extension point named runConfigurationExtension but not in the new one..

I have tried implementing a custom ProgramRunner but that never hits the execute() function when I debug so I dont think that is it.
Also tried implementing RunConfigurationBeforeRunProviderDelegate and adding log messages, doesnt seem like this is a way out either..

Any ideas on what extension point it could be through which I could modify the RunConfiguration? Thanks!