I created a little app drawer widget in Plasmate, but It isn't a button that launcher a popup app drawer, and the gridview extends beyond the widget boundaries...

If any of you would like to hack on this (or give me pointers), I've uploaded it here https://github.com/lunarcloud/plasma-appdrawer

You may also wish to ask for applet development assistance on the plasma-devel@kde.org mailing list.