Filling multiple lines of subform on add/ on load ?

Filling multiple lines of subform on add/ on load ?

Hello everybody. Is there any way to pre-fill three (or more) rows in subform ? I have Form lets call it "order" and there is "subform" with lookup "product". I need to have there three lines with products (which are very frequently used almost in every order) pre-filled. I did not find any solution in formums. I dont have any idea how the code should look like.