Instead of setting DRO to zero, save the current value of the DRO in your own variable. This is offset that you subtract from encoder DRO to get your new position, which you can save to a new DRO.

So, for example, you determine that the encoder value of 1234 should be showing 0. Save 1234 to a offset variable and subtract this value from then on. The encoder value of 1244 will then read +10.