Hi Tjerk.
I didn't tried but i suppose you send info to the lcd in 2 salves, the 4 left's bits and the fourth's right's bits.
i suppose you have to add a delay between the 2 "salves".
if you try it, give us feedback...
i don't find any tuto to communicate to lcd in 4bits, only instructions in the lcd's datasheets.
regards
eric