SR-NIEL cross section for electrons is included in Geant4 since version 9.5.
Starting from version 10.3 of Geant4, released on december 9 2016, is possible to select different nuclear form factors according to what is already implemented in SR-NIEL calculator:
- Exponential nuclear form factor
- Gaussian nuclear form factor
- Uniform nuclear form factor

Moreover the user can also choose to not use any nuclear form factor. In this case only Mott cross section is included in the scattering calculation.
To select different nuclear form factor a command is made availble to use in macro file:

/process/em/setNuclearFormFactor formfactorname

where "formfactorname" can take the following values: None, Exponential, Gaussian, Flat.
Further information about electron cross section and nuclear form factors is available at this page.

In the following graph, it is shown the differential cross section for 250 MeV electrons scattering on Silicon,using Geant4 simulations with the different nuclear form factors available.
The experimental data are from G. C. Li, M. R. Yearian, and I. Sick, Phys. Rev. C 9, 1861 (1974)

Geant4 FF