There is a trick, if you wanna cheat.
But there's a no-hack too.
Here's the no-hack one.
Give Howard a lot of minutes. Probably take out abt. 6 mins out of Gasol's minutes and sign Elton Brand.
You now have 2 good Power Forwards.
Now raise Elton's minutes and make him a 7th rotational player.
Throughout the mid-season, there is a 65% chance Howard is going to resign (depending on your team's performance. 41-0 = 80% signing. 25-16 = approx. 50% resigning)
If Howard doesn't resign on the trade deadline, and you really REALLY want him..
Cheat.
Edit Howard on your 'manage roster' option.
Press LB or L1 on your controller (depending whether it's X-Box or it's PS3).
Go to Year 2, or the next year after his last year with cash in it.
Raise it to abt. 15M-20M.
There you go. Dwight's auto-resigned.