I came across a special offer on KAKU outlets from some Dutch home depot, so I bought some and added a set of 433 MHz ASK modules to the cluster.

After doing the research on internet I found the following code for controlling the KAKU wireless outlets: http://weejewel.tweakblogs.net/blog/8665/lampen-schakelen-met-een-raspberry-pi.html

I works like a charm!