Hi Doug,
I kinda doubt that there is any way of "sealing" that top with anything, at least not for several months, and maybe much longer. That mineral oil will be well soaked in and I am highly suspect that it will not let anything stick to it which means what ever you coat it with will never really dry properly, it will just sit on top and just get wiped off.
If you let that top sit, and do nothing to it for ???? many weeks ??? or months ???. It possible that the the mineral oil will soak in deep enough that some time in the future, you "might" get a product to stick to it.
I have tried coating pre-oiled materials in the past without any luck .. hopefully you will do better, or maybe someone else has an idea or new product that might work.