Sorry to hear about this mishap...I often prop the carboy up on a big butcher knife handle while siphoning to hold it at an angle to get the last drop out...and...I have left for a minute hoping it wouldn't shift...think I might invest in one of those plastic wedge things invented for this purpose....
Hope you still have enough wine for the wedding.
NW, you might want to stay with the knife or possibly a shallow rubber doorstop. I have one of the plastic wedges and never use it anymore. It puts the carboy on too steep of an angle and it rocks like crazy-very unstable. I use a little plastic tackle tray about 3/4" high that works well. Of course there are more than one model of them, and I may have chosen the wrong one when I got it.
Oh, no Scuba,
That story just gave me a sick feeling in the pit of my stomach!!! Was it white or red? Was it carpet or tile? I guess that is why I always hold my carboy and tip it myself to get all I can out of it. I imagine that happening and then tighten my grip. Sorry you had such a mess.