Yep, that's exactly what I did (except I didn't cut out one side...he just hops over!).
And what really helped is to find an opportunity to soak up a little bit of his pee on the pad, and then place it in the box. That way it's already scented for him, so he is more likely to go on it. I just kept a bag of treats nearby so I could reward him every single time he went on it. Good luck!!!