In the early days we did it when he was on the change table. While changing him I'd sing an educational type song and after, while he was still lying there, I'd flash the cards. I'd also have a stack on the diningroom table and flash them just before he got down to play with Dad. Dad would stay at the table until it was done, too - that way there was no extra draw or impatience. Now we do it while he is on the potty - he doesn't sit still much anymore
But I'll admit that it doesn't happen with as much frequency as he's quite independant in the bathroom now.