When standing and holding an AR-15, I'm having some trouble following the steps to load it.  Basically, when I hold the rifle with one hand and pull the charging handle back with the other, I have no easy way to depress the bolt catch.  It would be best to have a third hand for this.  Have I missed some obvious thing here, or is this naturally a clumsy process?  Thanks.

Why do you need to lock the bolt back to the rear?  just insert a mag and cycle the charging handle.  If you must lock the bolt to the rear while standing, try this:  move forward hand back from handguards to the mag well, with that hand grip the weapon at the mag well while depressing the bolt catch with thumb (right handed version).  Then use your shooting hand to pull the charging handle.  Hope this helps.

If you are right handed, your left hand should slide back from the front handguard till it rest against the front of the mag well, index finger will rest on the curve where reciever and barrel meet.
That way your thumb can activate the magazine catch.
Turn the rifle so the ejector port is facing slightly downward, and use your right hand to pull back the charging handle.
The pistol grip will rest against your stomach, and keep the rifle from going back as you pull the charging handle.
I have smaller hands, and this method works well for me.

I am kind of confused about what you are asking. If you are loading an AR and the bolt is locked to the rear, there is no reason to use the charging handle. You insert a magazine and slap the bolt catch.
If the bolt is forward, there is no reason to hit the bolt catch. You insert a magazine and run the charging handle.
If you are doing a speed reload, you insert the magazine with your left hand while keeping the weapon up and on target. You smack the bolt catch with the heel of your left hand.
If you are initally charging the weapon, you keep the weapon pointed in a safe direction, insert a magazine with your left hand and run the charging handle by grasping the left side of the charging handle between your thumb and index finger.
The only time you would need to run the charging handle and manipulate the bolt catch is if you are unloading the carbine. In this case you would keep the weapon pointed in a safe direction, grasp the reciever in front of the mag well with your left hand, pull the charging handle to the rear with your right hand and press the bolt catch with your left thumb. Then with the bolt locked to the rear you can look and feel inside the chamber to ensure the weapon is in fact unloaded.

I guess i'm assbackwards then cause i wrap my right hand around the magwell and depress the bolt catch and run the CH with my left hand.

Thanks... maybe I'm following the manual too literally.  It says to lock the bolt to the rear, insert a magazine, and press the bolt catch.  There's some verbiage about "unsafe conditions" doing it in ways other than this.