I found this blog recently that had an excellent solution http://rapidminernotes.blogspot.com.au/2013/05/finding-next-sunday.html
I tried it and it worked - gave me a bit more of an understanding about how some of these rapidminer functions work.
In the end I wrote an SQL query on my "Read Database" operator because my process was already too long without the addition of more operators.
I'll play with date-to-nominal today and see what happens.
Thanks for replying!