I once found myself in a curious and not entirely dissimilar situation - the client was essentially paying a retainer to my employer to make sure I was available to do something for them asap if they thought of anything they needed (the product was in the final run-up to the final release).

The way the arrangement was worded meant that the client only paid for the hours I wasn't doing anything else that benefitted my employer. As soon as I started doing some analysis for another tender we were making, for example, the client stopped paying.

Consequently, being an ethical kind of person, I diligently earnt money for my bosses by doing crosswords, figuring out how to do sudoku, writing a program to do sudoku for me, reading books (some technical, most not) learning ant (vile), learning perl (much much nicer), and painting my front room (with the laptop under the dust covers, and the email alert sound turned right up).

Sadly, the paint we'd chosen didn't cover very well, so it took four coats. But I was probably the best paid decorator on the planet for a couple of days.

And when that contract finally ended, I resigned and went elsewhere, partly because they were being bought out by a company that wanted to take them in a completely different direction, and partly because I wanted to actually change something again...