This is not possible with VirtueMart out-of-the-box.
And also, it's really difficult to do it even if you hack the code. Delivery method is "per order" so how would you manage an order with different products which have different delivery methods?
Of course everything is possible with enough time and skill, but you should rewrite a large part of VirtueMart checkout. You may have a look in Projects, Modifications, Hacks and Tweaks forum, maybe someone already worked on this task.