The best thing to do is to just tint your eyelashes!

it sounds like you already have really nice thick long eyelashes.

You can get eyelash tints in most beauty salons.

Swimmers use it for example as they can't wear make up in the pool really.

It isn't very expensive and it's really quick to do. They can choose a shade you would like. For example a light/medium brown or a blue/black which is as dark as if you had mascara on. It's up to you what you choose but I think this could be the solution for you!