Wouldn't it be faster to simply cut the texture file in half and have one square texture file per uv space? I am fairly new to UV tiling myself, but it seems like a nice quick workflow when using multiple textures. Include u0v0 and then u1v0 in the filenames.

Edit: Alternately, I believe it might work in your place2dTexture node if you set the Coverage to 2, 1 (assuming your texture is twice as wide as it is high) and turn off Wrap U and Wrap V.