I assume that you have the
EnableAutoDiscoveryAndPing parameter set to 1 in your blogger instance's parameters?
Nope, the Blogger package cannot currently let you specify Trackback URLs. This is a Missing Feature. What it does support, however, is Trackback autodiscovery.
Of course the entry you are linking todoes have the Trackback autodiscovery code, and at first glance it looks correct. So please check the
EnableAutoDiscoveryAndPing parameter, and if it still doesn't work please file a bug (you can assign me to it).