Paste Every Nth Row

I have a large data sheet, around 8,000 rows. I need to be able to copy the data and paste it into a client provided template. The template is already pre populated with entries on every other row, so I need to be able to copy my data and paste it into every other row of the template. I've attached a simple example to show how this needs to work.

I also need the flexibility to be able to enter a different number, via a user entry box, because sometimes, the client supplied templates will have two rows of pre populated data, so I would then need to paste my data evey third row and so on.

Is there any way to achieve this?

Many thanks