Catalysis of the reaction: (E)-nerolidol + NADPH + O2 = (3E)-4,8-dimethylnona-1,3,7-triene + NADP+ + 2 H2O. It is unknown whether this reaction proceeds by the direct release of the 4-carbon compound but-1-en-3-one, or whether the substrate is first degraded to C11-geranylacetone and then cleaved to produce (3E)-4,8-dimethylnona-1,3,7-triene (DMNT) and acetone.