If your device is rooted, then it is very possible to do so using a third party application.
If you are not rooted and on stock ROM, then it is only possible to do if your manufacturer supports it in their android overlay.
For example in Android 4.4.2 kitkat on the samsung galaxy note 10.1 2014 edition, there was an option to adjust volume without the buttons, but the option was removed in the android 5.1 lollipop update.
HOWEVER, this app creates a widget instead and works in the same way as adjusting from the notification area
Slider Widget - Volumes on Google play
You should find the app in question.
Here is another one: http://nexus5.wonderhowto.com/how-to/control-volume-directly-from-notification-tray-lollipop-0159666/