In this paper, we propose TunnelSlice, which enables natural acquisition of subspace in an augmented scene from an egocentric view, even for scenarios involving ambiguous center objects or object occlusion. In wearable augmented reality (AR), approaching a three-dimensional (3-D) region including the objects of interest has become more important than approaching distant objects one by one. However, existing ray-based volumetric selection through a head worn display accompanies difficulties in defining a desired 3-D region due to obstacles by occlusion and depth perception. The proposed TunnelSlice effectively determines a cuboid transform, excluding unnecessary areas of a user-defined tunnel via two-handed pinch-based procedural slicing from an egocentric view. Through six scenarios involving central object status and different occlusion levels, we conducted a user study of TunnelSlice. Compared with two existing approaches, TunnelSlice was preferred by the subjects and showed greater stability for all scenarios, and outperformed the other approaches in a scenario involving strong occlusion without a central object. TunnelSlice is thus expected to serve as a key technology for spatial protocol and interaction using a subspace in wearable AR.