you can use to build the relationship during the pre-sell but i think it's more effective to user webinar to actually sell your product.

i recommend that first you teach some valuable lessons through webinars to your existing list in order to position yourself as an expert in their field.webinars usually have higher perceived value than teaching with normal how to videos.

then during the pre-launch phase you could offer to do webinars for your JV partners to help them in pre-selling to their list.a lot of marketers and gurus are using this technique.

so instead of doing the hard selling through the sales page you can webinar technique to do soft-selling tecnhique.you can demonstrate how to use your product works very good if you have software based products or teach them some of the techniques covered in your course.

it's kinda of teasing them to know more about their product and they would feel like buying it after learning all the tips and tricks that you have shown them