Chromecast Question?

So I go to a small school, and we have a distance learning lab, that we use to share a Spanish teacher with a nearby school, and we got a grant to get 5 TVs, but we only use 3 so my school wants to set up 2 TVs to just display a slideshow of announcements all day. They were planning to send an HDMI cable through the walls, which was going to cost a lot, but, I told my Principal about Chromecast last monday, and he was excited because the ~$70 for chromecast is a lot less than they were planning to spend. Unfortunately (perhaps fortunately) they were sold out, so he asked me to bring in my Chromecast when it arrives.

My Chromecast arrived yesterday, and it works exactly like I expected except for one thing: if I am castingsomething to the TV and someone decides to cast something else, the new thing will get casted to the TV. My school has a one-to-one computer program, so every student has a laptop connected to the wireless, and would be able to change what is being casted on the TV. Is there a way to lock the chromecast to just one device? the only other solution I can think of is to dedicate a router to the just the chromecasts, which may or may not be cheaper than sending an HDMI cable down the hall from the office to the TV. If you can think of any solution, that would be great, and you could consider it community service, because you are saving my school money.

Thanks