Nipype fslmaths intensity normalization

In the standard FSLMATHS implementation in FSL, there is a parameter -inm to do intensity normalisation (per 3D volume mean). It is not clear to me how this is implemented in Nipype.
Checking the manual at Neuroimaging in Python - Pipelines and Interfaces — nipy pipeline and interfaces package did not show the same parameter. Could anyone help me how to do this in Nipype, or a way around using a different computation?