If you've got lsxcommand someplace, type it there. If you're using RabidVWM, select the text here and drag&drop to the vwm. There's probably other places, but IMO themes without some sort of command box are lacking.

If all else fails, press ctrl-alt-f1 and select "run." Click "Browse..." and find litestep.exe. Still in the run dialog, type a space at the end and paste in the command after that. Then tell it to run that.