Skipping address form for specific product on my shop

[localh0st]

Hello. I've got problem- I've got one product which is free, and I want skip address form input for users who didn't fill it yet and order the free product. 

Actual ordering steps for newly registered user:

 

register (name/surname/email/password) > product order > complete address forms (domain.com/address?back=order.php?FStep=multi-shopping)> list of products in cart and submit (release) button (domain.com/quick-order)

I want to cut this way, and for my free product I want make:

register (name/surname/email/password) > product order > product ordered/transaction finished (just like clicking submit button from last step from above).


I divided code in product.tpl, so I can manage which product is free and which is not. The button's code for order the free product is:

<button type="submit" name="Submit" class="button_green_medium" {if (!$allow_oosp && $product->quantity <= 0) OR !$product->available_for_order OR (isset($restricted_country_mode) AND $restricted_country_mode) OR $PS_CATALOG_MODE}disabled="disabled"{/if}>{l s='Buy now'}</button>

What's the simplest way to finish order transaction just by clicking "Buy now" button (and avoid functions from  AddressController etc.)?