U can't map 2 keys/buttons to Lookback, or any view besides look forward. At least what I think you are asking is... map a view to lookback, then adjust lookback to look left of the tail, save it to a key and then adjust the view to the right of the tail and then save it to a different key.
U can press F9 once in flight and get instant snap views, which u can do much faster than in reality, unless you are Linda Blair...
SKurj