There is a way, but it's very counter-intuitive.
- Edit the desired customer in the backend.
- Click on create order
- Select one of the stores
- Click on the "Add products" button on the right.
- Find the products you want to add to the wishlist and check the checkbox on the desired rows.
- Click on "Add selected products to order".
- On the dropdown near each item you should see an option "Move to wishlist". Select it and click on "Update Items Qtys".
But there is a catch.
It only works if the customer already has a whishlist. It can be empty but it has to exist.
To check this, you have to look in the
wishlit table. Search for a record with
customer_id = your customer id.
If there is none, it won't work. But you can add it with a simple insert in the same table.
If this is not a suitable solution you can try to login as the customer and add his/her products to the wishlist.
Here is a full functioning module that allows you to do that.