The same techniques apply as with classic UTAU.
You can try using extreme vibrato settings with a very short cycle. This will work better if you're using the classic renderer and a resampler other than worldline.
Some resamplers have growl specific flags, like Moresampler. For others that don't, you can use utaugrowl. Make a copy of the utaugrowl.exe in the same folder as the resampler, then rename it to match the resampler but with _ug at the end (for example, TIPS_ug.exe)
For the most realistic results, pick an UTAU voicebank with real recorded scream or growl samples. I recommend using tn_fnds or macres, which will loop the sample for long notes instead of stretching them.