I think I'm just too short and fat for that
if I don't have my legs straight the baby's butt is on me, and if I have them straight I can't bend over and reach their butt or reach to hold their legs up.
I either do it really fast and have their feet bent in front of their chest before they know it (and I have leverage to hold them there without letting them do the stiff as a board thing) Or I hopefully can get some one to come running quickly with cries of HELP POO!!!!!
I do also do the sit beside them with a leg over their chest if they are older toddlers who are cranky and overtired and not wanting to lay still a second.