Using FRP and IORef in threepenny-gui

Question

I have a little example using IORef in threepenny-gui (TPG):

testIORef :: IORef String -> Window -> UI ()
testIORef ref window = void $ do
    return window # set title "Test IORef"

    inCell  <- UI.input
    outCell <- UI.input

    -- When value changes write to IORef
    on  UI.valueChange inCell $ \_ -> do
        inValue <- get value inCell
        liftIO $ writeIORef ref inValue    

    -- function that reads the IORef and sets the value of an element with it
    let setValue oc = do  
            newVal <- liftIO $ readIORef ref
            element oc # set value newVal

    -- When enter is pressed update the value of the output
    on UI.keydown inCell $ \c -> if (c==13) then setValue outCell else return outCell

    getBody window #+ [ column [ grid [[string "In cell :", element inCell]
                                      ,[string "Out cell:", element outCell]
                                      ]
                                , string "Cells should update while typing."
                               ]
                      ]

I am trying to change this to use the Reactive stuff in TPG. I have got as far as making the Behaviors from the events valueChange and keyDown:

inValue <- stepper "0" $ UI.valueChange inCell
inEnter <- stepper "0" $ fmap show $ filterE (\kc-> kc==13) $ UI.keydown inCell

But I am stuck on how to use these Behaviors to save/get the value to/from the IORef. The problem is that the IORef calls will be in the UI monad, so if I use them the Behaviour will be Behavior (UI a), but then they won't work with sink. I know in this case I needn't use an IORef (eg. the currency conversion example) - but in my actual case I do.

EDIT: I tried writing my own attribute:

valueUI :: ReadWriteAttr Element (UI String) String

so that I can set an attribute with a Behavior (UI String):

inEnter <- stepper "0" $ fmap show $ filterE (\kc-> kc==13) $ UI.keydown inCell    
let getValue = fmap (const $ liftIO $ readIORef ref) inEnter   
element outCell # sink valueUI getValue

The code compiles but doesn't work.