From what I've tested, that only supports one image at a time.I'm not certain (not read all of the docs), and maybe you've tried it already but I'd assume this would work:
https://szs.wiimm.de/wimgt/
not converting 1 image multiple times (you're right, could just automate), but converting multiple images into one single fileAre you just trying to avoid running multiple single commands? Or even with using single commands repeatedly are you unable to achieve what you're after? If the former, we can write some batch code to automate converting multiple singles. If the latter, then sorry, I'm not sure of a tool that does this
wimgt ENCODE myimage.png -d myoutput.tpl -x TPL