Combining products with different quantities

I´m building a shop to sell language courses, using the Hikashop Business edition. Each item is a course week and the customer can buy, for instance, 1, 2, 3 or 4 weeks. Besides, for each course (regardless the number of weeks he books) the customer pays a one-time registration fee. That means that a customer can buy 4 course weeks and 1 registration fee.

I would like to know how can I accomplish this. I have tried with options, but in this case, the registration fee get multiplied by the total number of weeks. I can't do it with characteristics either, because here I cannot put a price for the registration fee...

I thought, maybe it's possible to tie both products (course + registration fee) so that by buying the course you have to buy both, but I can't find the way to do it. Before Hikashop I was using Virtuemart and that's how I solved the problem, but now I'm lost. Any idea would be appreciated. Thanks!

Hi there,

I don't see a solution to do this easily for now. We have a feature on our TODO list which will allow to add a product to the cart according to the user group but it's not done yet.
Actually the only option I see is a custom code which check during the checkout if the client have buy or not the registration product. If not, it add the product to the cart.
If you have some php knowledge it shouldn't be really hard but if you don't I suggest you to ask on the commercial job forum.