How do I make a conditional helper with ember-cli and handlebars 2.0.0?

I am trying to achieve something similar to the form of:

{{#if has-permission "my_permission"}}
    // do some stuff here
{{else}}
    // fallback
{{/if}}

OR

{{#hasPermission session.user.permissions "my_permission"}}

I cannot figure this out. I've read this but there isn't much explaining on anything other than helpers that render content or alter it e.g. {{render "something"}}

When I try to make it a conditional I get this:

registerBoundHelper-generated helpers do not support use with Handlebars blocks.

Any help greatly appreciated, thanks!

PS Im using ember 1.9.1, latest data and handlebars 2.0