Two input streams sounds like a good hacky solution. One input stream captures everything, the second is on the look out for your filler words like "um, aahh, waaiit, no nevermind, scratch that". The second stream can act as the veto-command and cut off the LLM. A third input stream can simply be on the lookout for long pauses. All this gets very resource intensive quickly. I been meaning to make this but since I haven't, I'm going to punish myself and just give the idea away. Hopefully I'll learn my lesson.