Those already stick out a further 16mm than the rays wheels on the rear. I use this website for offsets: http://www.1010tires.com/Tools/Wheel-Offset-Calculator
As its suggested that the rays have a 25mm spacer, you could get a 10mm spacer but I wouldn't recommend any more than that. The fronts however only stick out a further 1mm, so you could get a 20mm on those.