I don't know about the honey substitute. What's in it? Agave nectar is a honey substitute (so I've just found out) and is mostly made up of fructose, which is a different type of sugar from table sugar, but is still a sugar. I wouldn't vape it. And as a general point I would advise against
vaping flavourings not specifically intended for
vaping purposes unless you really know your stuff. Sugars should be avoided because, as far as I know, they don't vaporise. In other words they don't turn into vapour, they just caramelise and burn in your atomizer, potentially giving out harmful fumes.
There are many vendors of flavourings that have been developed with
vaping in mind. For example
this is a well known flavouring vendor that has caramel, honey, and various other sweet flavours. But note DIY juice mixing is not really for the newbie unless you are
very comfortable with what you are doing - have a read of this -
http://www.e-cigarette-forum.com/forum/announcements-rules/144783-warning-e-liquid-diy-safety.html