If you larksheaded the fixed eye of the whoopie sling on a toggle and then put the continuous loop on the knot and not the toggle
, it would work but to connect the loops to the whoopie slings I'd recommend against using knots. Also a simple larkshead of the whoopie slings fixed loop on the continuous loop itself would hold but knots can derate the strength of the amsteel by a signicant amount.
To be able to quickly connect and disconnect the two take a look at Dutch Biners
. They say 400lbs but IIRC Dutch tested them above 1000 lbs or something like that. If you made your whoopie slings yourself you can also undo either of the loops on the whoopie sling and insert a Dutch hook
. Of course you could always go to an outdoors store and pick up some light weight climbing carabiners.