Detect shipping method in checkout procedure

Hi there Opencart Community! first i'd like to thank you for the great job you have done and you're still doing with opencart.
I'm trying to solve this problem here
http://forum.opencart.com/index.php/topic,1067.0.html
What i'd like to do is to show/hide some paying method if the customer select a certain shipping method

i thought i could do this via template, with a simple if-else. but i need to retrive which shipping method id the customer selectd,and make it "avaiable" inside checkout_payment.tpl

my idea to modify the template is probably wrong, i should probably work inside the catalog/controller but i dont know how...

any suggestion? even the smallest one will be appreciate