Trying to calculate how many bitcoins is a KwH is kinda like trying to find angels on a pinhead.
I do not think it is that hard to estimate. I did this a while back when the difficulty was 1,564,057.
The average number of hashes per block is difficulty * 2^32, for example 1,564,057 * 2^32 = 6,717,573,664,079,872 = 6,717,573,664 Megahashes/Block
Using an estimate of 2.3 Megahashes/Joule (a good GPU) yields 6,717,573,664 / 2.3 = 2,920,684,201 Joules/Block
Finally 2,920,684,201 Joules/Block is 811 KWh/Block
In order to include cooling and other losses double this number and round down to make the math easy, how about 1,564 KWh/Block at a difficulty of 1,564,057At the current difficulty of 1,250,758 I would estimate 1,250 KWh/Block.