You have a few options that would sort of allow you to do this:
 You could set up a processing template with your DRS action and a python action including any additional calculations you want to add.
 You could run the drs and subsequent calculations all via a script, e.g.,
drs = data.dataReductionScheme('U-Pb Geochronology')
settings = drs.settings() # a dict of all the drs settings, could print to see options
settings['ReferenceMaterial'] = 'Name of ref material'
settings['BeamSecondsMethod'] = 'Name of method'
 I've just added a signal that you can connect to in order to run functions after a DRS finishes that'll be in the next release. To use that, you would do something like:
but you would need to run that script once and be aware of making that connection multiple times (i.e. you could end up running your calculations several times).
All the best,