The Worm Sex Position is the Missionary position with the receiver on top but facing the giver's feet. Getting into the position is a little trickier than usual. The giver lies back on the bed and has the receiver sit on top of them, but as the position will put the penis at an unusual angle from the giver's body (i.e. pointing downwards) it will be easier if the receiver inserts from a seated (facing away) position, and then carefully lays forward while sliding their legs back toward the giver's head.
Care should be taken to not strain the penis further than it is comfortably capable of flexing!