I'm not sure how many people will benefit from this, but here goes...
It is possible to update a live LinuxMint with Keryx, provided the live OS has been given persistence. The process is made easier by creating a separate fat32 partition on the flashdrive, or using a Kangaroo flashdrive that has a slot for a microSD card as well (I found these at Newegg.). The Keryx would go on the fat32 so that you can run it from any OS.
I have tested this on Linux Mint 7 and Ubuntu with updating through these as well as a M$ Windows machine.
This is part of a larger project for me, but I thought someone else might find use for it. It could come in handy when you are using a network that doesn't play well with live OS's and want to get the updates.
http://keryxproject.org (I came across this open source project recently and it is incredibly helpful if you need such an application.)