walk her around a little bit before you take her up there.
i was told my gal ALWAYS pooped on the stand when i bought her. she's done it once this whole time.
i figured out to get her up and moving (so she poops there), i go and do a few things around the yard, THEN got and get her to milk. if she is laying down and you walk her directly there then i'm guessing she is more likely to poop on the stand.
Our 'regular' milkers rarely do, but the 'occasionals' (boers I'm milking colostrum out of or who are just there to get hooves trimmed) seem to poop on the stand more often.
I'll try walking her around first, but I open her stall and she runs immediately to the stand. Maybe I'll call them out to their yard for a bit of hay first instead of putting hay in their stalls. Make her move around some.
My DH does the "back scratch" on the does next in line for milking (it helps keep hair out of the milk bucket). They love the scritching, and if they gotta go, they go. Right after he finishes the scratching and moves to the next doe. It's kinda embarrassing for him, though. Sometimes they even go just when they see him coming. That embarrasses him even more.
Even when I milk alone, it is the same routine ... the girls get hooked up to their tie out. They know their places in line. Even without the back scratching, they usually pee and poop shortly after being hooked up. They only time I've had a problem with poo on the milk stand is when the girls hop up on it early. And stand there hoping to be first. Funny thing is, the first girls never do it! They know they are first, apparently, and never rush the stand.