There's no point in using Chosen as your main Melta platform with Iron Warriors when it's Havocs and Oblits that get Tank Hunter. But without Marks, you're very limited. I'd go with a less is more strategy here for the Chosen and make sure your Sorcerer, Lord and Warpsmith all have different strengths. For instance, give your Lord Fleshmetal and a Sword and 4++, making him you generalist beatstick while your Warpsmith takes the Armorbane Axe for moping up squads or beating down tanks and such and your Sorcerer takes a Force Stave for some Instant Death at S6 for MCs.
The Chosen themselves, I might give them two Meltaguns and bump their numbers up to seven, that way the HQs make it an even ten and they have a total of five meatshields. Slap them in a transport, Land Raider is my preference but a Rhino might be all you can afford, and pick a target of opportunity. It's not going to be very good, so make sure to beef up your Havocs and Oblits to soften up your opponent by the time this Chosen squad reaches them. That way this ridiculously priced unit killing some 200pts seems like a good trade. Turn them into a wannabe Death Star and you should atleast have a good time running them.