I think I get it. The original phrase is "quicker than boiling asparagus." The time it takes to cook asparagus by boiling it is pretty quick. So anything that takes a little bit of time may be done quicker than boiling asparagus. But the quaint saying in the OP assumes the sense of speed is the change of position rather than time to cook.
No, I wasn't familiar with Morituri te Salutant. But apparently the writer of the book I was reading is! That's interesting about Augustus coining phrases all the time. Presumable more intelligently than 'yuuuge' and 'bigly.'
