Just bang their arms blue with saam sing. Get their legs sore in static stance training. Add an assorted 2-3 other lin gung exercises which are typical to hung kuen like kiu sao with iron rings. And make clear this is stable Hung Kuen training and make the viewers aware of how long one should be able to perform these. Putting advanced students aside of those two hosts who do the full length/power and that should be pretty clear
I think the real prob is with how to organise the fight. Real hung kuen can't be done at full power IMO. Full power and you trade in a lot, making it more sanda. Difference between a dirty combat art which imho Hung Kuen is and a martial sport.
This last is a good discussion on its own we should do in a separate thread... How do you spar in your kwoon (if you do at all, bwaaa, speak of can of worms), how is it set up, etc.