Variable machine disk size

Hi Firecloud Team,

I am very confused about variable disk size in firecloud WDLs

My use case:
workflow inputs - (array of files)
required disk size - (total size of all inputs)*4

I found a similar question, but it was unanswered:
http://gatkforums.broadinstitute.org/firecloud/discussion/9347/size-arithmetic-issue

Is this currently possible in firecloud, and if not, what is the recommended alternative if there is one?

As a workaround I am currently writing a python script to make google api calls for each of the inputs to query the size and write an annotation with the sum, although this seems clunky.