There are lots of ways, but some will work better than others on different male subs.
Some ways require no touch at all.
For ways that allow touch, there are many!
Ejaculation and erection can be fun to play with. Neither is necessary for orgasm, although many men do not know this.
Many men are capable of multiple orgasms just as many women are, if properly taught. Stimulation of erotic zones all over his body (while avoiding the penis) can bring surprising results. This often will take time to teach him. You may need to bind him.
Tantric exercises can help.
Everyone has their own "hot" buttons, their own personal powerful turn ons. One sub may orgasm while being caned. Another may orgasm while his nipples are being loved. Another may come while his nipples are tortured. Some may orgasm serving their dominant orally. Others may orgasm from being taken anally. One sub may come from the touch of the lingerie you "make" him wear. Another may orgasm from your scent in your worn undies. Another may "fly" when "made" to lick you clean after another male ejaculates in or on you. There are hundreds of other examples.
There are no simple things which always work on everyone. You will find out through experience what works best and most cosistantly on your sub.
The scent, taste sound, feel and vision of the submissive's object of affection are all good methods of arousal.
Training him to react to your commands takes time. It may or may not work for a given sub, if the only stimulation given is the commands.
As always, your mileage may vary!