I ended up creating a PlaneGeometry with 3 segments along the width and height and deleting the middle faces like this:
var geometry:PlaneGeometry = new PlaneGeometry(100, 100, 3, 3);
//
geometry.subGeometries[0].indexData.splice(24, 3);
geometry.subGeometries[0].indexData.splice(24, 3);
geometry.subGeometries[0].updateIndexData(geometry.subGeometries[0].indexData);
I’ve adjusted the hole size by moving the vertices like this:
geometry.subGeometries[0].vertexData[15] = -40; // x
geometry.subGeometries[0].vertexData[17] = -40; // z
geometry.subGeometries[0].vertexData[18] = 40; // x
geometry.subGeometries[0].vertexData[20] = -40; // z
geometry.subGeometries[0].vertexData[27] = -40; // x
geometry.subGeometries[0].vertexData[29] = 40; // z
geometry.subGeometries[0].vertexData[30] = 40; // x
geometry.subGeometries[0].vertexData[32] = 40; // z
//
geometry.subGeometries[0].vertexData[23] = -40; // z
geometry.subGeometries[0].vertexData[26] = 40; // z
The resulting plane is attached.
