Re-fetch with Repa and Stencils

Question

I wrote a simple bilinear image resampling algorithm with repa, and since I need to use partitioned arrays to make it correct, I thought that I would go the whole swamp and with the help of stencils, too, hopefully get faster cycles.

From my naive understanding of how mapStencil works, I don't think this is enough for my task. I need something like transformStencil. I guess I need another Stencil, so I could have the old index and the new one.

Is there an easy way to re-fetch image replication in Repa? If not, how difficult would it be to crack mapStencil into transformStencil or something like that.