How to display a custom welcome message within a page

Hi there,

I would simply like to display a custom welcome message on a page of mine... "Welcome back USERNAME-GOES-HERE!"

However, I need to make this happen within a shortcode as follows:

[call_to_action title="Welcome Back, USERNAME-GOES-HERE!" tag_line="Good to see you!" button="Get Stuck In" link="http://bla.com"]

I found this but I can't really work out how to implement it:

http://spyrestudios.com/wordpress-tutorial-display-a-user-welcome-message/

Any ideas?