Well you already know about the VP/PT, and there's always the ego USB battery that can be used as a passthrough, but will always be 3.7volts. http://www.vaportalkstore.com/products/Joye-eGo-USB-Passthrough.html
You could try MadVapes, they have some interesting acrylic 5volt passthroughs. http://www.madvapes.com/USB-Passthroughs_c_164.html
There are also other 5volt passthroughs that are made as attachments to mod, like this one http://www.ecigsupply.com/Mod-Parts/Indulgence-usb-passthrough-p344.html used with mod http://www.ecigsupply.com/Mods/The-Indulgence-p342.html
Or this passthrough http://ikenvape192.corecommerce.com/The-Chameleon-Line/Chameleon-USB-PT-Pass-through-p35.html used with this mod http://ikenvape192.corecommerce.com/The-Chameleon-Line/The-Chameleon-p16.html
I hope that helps.