Sometimes you can use a 20 L (5 gallon) starter--it's called re-using the yeast cake from the previous batch you brewed.
I just saved myself the aggravation of cleaning out one of my fermentors by pitching a small beer (strong scotch ale second runnings) onto a belgian wheat yeast cake. I wasn't going to let all that leftover malty goodness go to waste by dumping the grains, so I partigyled. Not my first choice of yeast (WY3942), but it was what I had just brewed. Going to call it a Scottish Wit. Well...I dunno; there's no wheat in the grain bill, so it might have to be called a Scottish Witless. Have I created a new beer style?
pretty sure the wit refers to color. but you could call it billy collins. (a scottish wit)
**EDIT to correct my miserable cultural reference**
Rather than Billy Collins (an American wit) you can call it Billy Connolly (a scottish wit)