Ok, my sister just went through all this so I'll give you the short version -

IF he is still being a twat after bubs is born, and you have made it clear you expect him to sign it, you send in the birth cert signed by yourself.
They will contact you soon after asking why it is not signed.
You give him his details (name, address), they will take it from there and you don't have to worry about chasing him.

SO you call the child support agency (the details should be on any Clink forms you will get), and let them know his details and that you would like them to collect on your behalf.

THEN you give all bubs details to Clink (for your FTB and Baby Bonus), you let them know you have taken action to obtain child support, they will liase with CSA and you don't have to worry.

AND you still retain full FTB entitlement, and the CSA will stick the child support in your account - no fuss, no muss.

good luck with it all, sorry he is being such a tool.