No, you can not, and this feature is not on the road map at the moment.
Just going to point out two things, which might be non-obvious, but are good to keep in mind:
1) Any modification you make to the gateway, that were not at recommendations of support, or by following instructions of an SK, invalidate your configuration. From purely human perspective, you make some changes to the gateway, how do you expect support engineers to know what you did, and what the effects of it are? This is on top of the fact that you are modifying authentication mechanism (pluggable authentication module), which means that if you get it wrong, someone could log in into your gateway, or get permissions you don't want them to.
2) Setting up authentication on the gateway once is fine, but if you have to modify the settings on the gateway each time, you might as well set up local users. Those are supported. If you want new feature, don't kludge it yourself, push to get it as an RFE, then based on success of RFE, push to have it included in Jumbo HFA or new release, and supported out of the box.