I know that electric pianos can never compare to keys, hammers, and strings... But there are still dynamics, and basically you just have to develop more awareness of volume during your practice.
So, play around with dynamics... Practice playing your scales as softly as possible, using minimal force. Every instrument is different for the amount of force it needs before it will even sound a note, but to develop a sensitivity for controlling the force of your notes playing as quietly as possible is great. Once you can control super-low volumes, it's easy, almost second nature to control the gradients between. Try it!