We report a measurement of the CP-violation parameter φ1 obtained in a time-dependent analysis of B0→D(∗)0h0 decays followed by D0→KS0π+π- decay. A model-independent measurement is performed using the binned Dalitz plot technique. The measured value is φ1=11.7°±7.8°(stat)±2.1°(syst). Treating sin2φ1 and cos2φ1 as independent parameters, we obtain sin2φ1=0.43±0.27(stat)±0.08(syst) and cos2φ1=1.06±0.33(stat)-0.15+0.21(syst). The results are obtained with a full data sample of 772×106BB pairs collected near the (4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider.