Hi André,
Thank you for your answer, I have made a post on the HP 3PAR community site and got a solution close to yours. (http://h30499.www3.hp.com/t5/Storage-Area-Networks-SAN/3PAR-LUN-does-not-shrink-in-size-when-VMware-virtual-servers/m-p/5936325/highlight/false)
Kind regards,
Carl-Marius