There is absolutely no way that an OWB rig can be concealed as easily as an IWB rig. Period. The main difference is that the IWB setup smooths out all the lines of the holster and pistol so it doesn't print as easily, and even though the grip is above your belt, it is pulled into your side much better and flatter than any OWB rig can.
So my first suggestion is to "get used" to an IWB rig. The people who have the most trouble with doing so is because they don't want to change the way they dress AT ALL so stuffing an IWB rig down your pants is sort of like shoving a thick paperback book in the same place.
To be comfortable with IWB wear, you should start buying your pants one size larger in the waste as well as to get belts that are about 2" longer than you have been. The moment you add the little extra space you need INSIDE your belt for the IWB rig, you'll hardly notice that it's there.
My second suggestion if you simply refuse to even try to accomodate IWB wear is to make sure that you have the very best OWB holster you can buy. Leather is the only material you should consider it be made of because it can be made to be very "stiff" for pistol support, but will also blend better to print less than any of the plastic ones. One I like a lot because I like how they slant the belt slots inward at the top for better support is the Brommeland:
http://www.brommelandgunleather.com/Products/def-con.htm
I don't carry OWB, but if I did, that would be the one I'd go with.
There are several holster makers that make good ones other than the one mentioned above, but what you need is secure holster that will pull the pistol in and keep it there.
Also with an OWB holster, the belt you wear is every bit as important as the holster itself because it's the belt that keeps the holster securely where it is and should stay. And I'm not talking about an "expensive" belt from a department store, I'm talking about a REAL GUN BELT of the kind you can get from most high quality holster makers. For IWB wear, a 1-1/4" belt is fine because it would be plenty stiff to keep everything in place, plus I like that size because it doens't "look" like a gun belt.
But if you're going to wear OWB mostly, you NEED to go with a 1-1/2" belt because, again, with OWB wear, it's the belt that does ALL the supporting of the holster and pistol to keep it pulled in and in place. A 1-1/2" gun belt with the Brommeland Def Con would be a perfect setup (but again, there really are some other good holster makers around nowadays).
A cheap holster and/or belt will allow the pistol to lean outward where the grip will look like you have a telephone pole sticking out your side.
Then after you have a good holster and belt, go buy an entire wardrobe of oversized Hawiian shirts with the loudest, tackiest prints you can find.
Carter