Using phpbay within “custom fields”

I’m trying to set up a new wordpress theme and I want to use a custom field to use with the phpbay plugin. So I’ll create a post, and then enter the relevant phpbay tag into the custom field to display it on the site. Is there any way of doing this?

I’ve got the custom field set up properly, just can’t get the phpbay tag to work within the custom field. Any ideas?
Ideally I’d like to auto populate the phpbay tag with the post title (although since I can’t even get the tag working in the custom field I haven’t even attempted this yet!).

Any help appreciated.
Thanks