Woocommerce and Gravity

Hi,

I have a woocommerce’s shop selling books and DVDs set up with paypal for payments. I have also a donation page with 3 forms created with Gravity and set up with Paypal as well.
My problem is that the shop and the donations are separated. I mean that one cannot make a donation and buy a books at once.
How can I get the donation forms buttons to direct into the woocommerce cart?

here’s the shop page: boutique

Here’s the donation page.

Many thanks for any help…

https://ww.wp.xz.cn/plugins/woocommerce/