get a tool that does it. ie: paragon partition manager server edition. acronis also produces a server edition. most generic partition tools will NOT support servers. paragon is in my opinion superior. i believe you can also download a trial version which will allow you to do what you need without having to pay.
the paragon server software will allow you to create a boot cd that will take your active partitions and allow you to extend like you want. all with zero threat of damaging their partition tables, data, boot record, etc.
