blocking air intake

I just put on the cowl snorkel like the one on Madxj.com and I wanted to be able to cover and uncover the stock intake when I wanted. Has anyone come up with an ideas for this?

sorry no answer but I want to do the same on a temporary basis for that odd "dodgy" river crossing maybe in conjunction with a radiator blind (or sheet of something) as I don't want to have a snorkel. So if anyone answers will they please consider that as well. Hopefully this doesn't steal your thread!