I did exactly this. I am on work permit and my hetero unmarried partner came with me. He is considered a work permit dependent, not an unmarried partner. He has clearance as long as I do. I am on a 5 year WP, so he has a 5 year visa as well. We had to provide the same documentation that is listed for an unmarried partner visa, but when you fill out the VAF1 form, you check the WP dependent box.
You must be living together for 2 years consecutively, but are allowed up to six months apart. The Consulate tells you that the 6 months is for something big, like caring for a sick relative, but I have heard of people getting by with just a normal separation. I can't say for certain that it would be approved for less than the 2 years, but I do know of others that have been ok.
Good luck.