I don't know if this will help ...but i ocean sail a bit ...and sometimes i have to downhaul out to sea .but the best way is to sit on your board
un attach the extension from the base..foot on the extension and pull on the downhaul ,..in your case the base would be easier to connect to the board ,by disconnecting the base ....just don't drop it ..

..that way you have your weight to steady the board and two hands free to connect the sail again ,oh one foot holds the sail so it doesn't drift away ...i saw a big black shadow under me last time i was down-hauling. out at sea ...might of been a long turtle ? ..