How can I ejaculate without direct stimulation?

Prostate massage. I'm assuming you mean without penile stimulation.

Yes try prostate stimulation, you will be surprised how aroused you will get, it is your male G spot, and I know a lot of guys don't admit to it, What most men are far less familiar with is their own male G-spot.if you keep a open mind it could lead you to one of the best orgasms you could ever hope for.

The male G-spot isn’t all that difficult to find, but it does require a little patience. Lying on your back is generally considered to be the most comfortable position for this, so you’ll probably want to make use of the bed or perhaps a large sofa. The process will be easiest with your legs elevated, which you can do by simply leaning your legs against the wall behind the bed or draping them over the back of the sofa. If you’re still having difficulty reaching the perineum from this position, you can lift your backside further by sliding a pillow or two under your bum. Use the soft pad of your index finger while exploring, and be gentle. As you relax further, lube your finger up and let it gently brush across the surface of your anus. Repeat this move several times, each time increasing the pressure slightly. When you’re comfortable enough to begin probing, you should keep things slow and gentle, taking care to relax your sphincter during the process. Once you’ve come in contact with the male G-spot, you’ll recognize it as a small, chestnut-sized bump situated approximately two inches inward.

Don't be ashamed of stimulating the male G-spot; the results can be explosive.