You know what I do when I need Lily to last longer than she would normally?
SUGAR!!!!!
Lily doesn't have anything that isn't naturally sweet, well not very often anyway, because it sends her quite hypo. So I have used this to my own benefit at times and kept her going with some white chocolate
If she is dog tired its not enough to send her hypo but gives her the energy to keep going that little bit longer. Of course you have to watch they don't go into the sugar rush slump, but it does work, providing you can keep them going until they get something healthy in them to balance the sugar levels back out.
Maybe not the answer you where expecting but hey, if it works