I have A05 bios, and no, there is no option to boot from the SD slot.
But I successfully used SD cards to boot using a Sandisk MicroMate SD USB adapter (came packed with some SD cards bought some time ago).
So now I have several 8GB, 4GB, 2GB SD cards with various filesystems and boot options. I used one 8GB SD-HC (class 4) card to install Mac OS X.
This lets me have 2 cards mounted, one in the Mini's slot the other in the adapter. Great for copying across 2 cards and hd. Found that getting an 8GB SDHC card was cheaper than an 8GB USB stick, and much more convenient.