You can, and it wouldnt be that hard to make but I think it will look awkawrd and dont really see the point of doing this.
Is the pump battery operated or something? so you can run it when the power goes out, or just to refill the empty case when you loose power?
I dont know how much you loose power but filling it up isnt that bad.
It may be kind of hard to regulate the water flow into it but i dont know exactly what you want to do/why.