Using the Skin Weights Import/Export Toolset

1) Select the mesh w/a Skin Modifier applied and run the Skin Toolset. Export either all the weights or selected weights to file. (To Export selected weights, open Editable Mesh and select the vertices to export)

2) Either attach the second half of the mesh and import the weights via vertex position, or import the weights via vertex index if not changes were made.

3) To import and mirror the weights, select "Create Mirrored Bones" to add the mirrored bones to the skin influence list and align the mesh so it faces perpendicular to the X axis. Import the weights (either using Distance Check or Threshold check) and voila.