Even better, don't worry about an airlock at all. Take it off and just cover the top with some sanitized aluminum foil. For a starter, you want as much oxygen as you can get (the exact opposite of your main fermentation).
As for the heat, it could have set the yeast back but, since you are making a starter you should be fine. The one thing, though, is that, because of the setback, it's probably gonna take more time. Have patience and you'll probably start seeing a nice slurry forming.