MarketPress: Ensure more customers & ease of registration

So I want users to be forced to login in order to make a purchase in MarketPress. I want to use part of another plugin, "Premium Membership" to force users.

When they get to the part where they must either login to continue or click register I wish to change the "Register" button to a popup registration page, similar to the one in "Premium Membership" plugin.

This is currently how the prompt to login or register looks within MarketPress when forced to login:

This is how I would like it to look when prompted to login or register to continue: - This screenshot is from the login/registration process of the "Premium Membership" plugin, and since you already have this code made it shouldn't be hard to add it to the MarketPress plugin.

Upon logging in or completing registration I would like the cart to continue to the next step that it would if the user was logged in in the first place.

The benefits of this feature would be that you would not lose as many customers due to forced login, as they are not required to leave the page or have a long annoying registration process.

Also allowing users to choose their own password when registering skips the email verification process which leads to a higher chance of losing the customer. Currently in the plugin when a user clicks register they are not directed back to the cart after as the plugin depends on wp-login.php

Some of you staff & developers may have noticed I have started some other discussions on changing the shipping form fields so that it grabs native registration info from a logged in user, therefore making sure the products are assigned to the user who paid for a product.