I noticed something today. If you right click with the mining drill (only checked for the diamond version) on a block and you have torches in your inventory, it places a torch. It's a little odd, but it makes sense, as you can mine away without switching tools.
Then I was cutting some trees with the chainsaw and thought it should be able to do the same thing with saplings! I propose that if you hold a chainsaw and right click (NOT M-right-click) on a valid block while having saplings in your inventory, it will place one. Of course, since there are multiple types of saplings there'd be an issue of priority. I suggest going through inventory slots in order, with preference to the tool bar first, until saplings are encountered.
In this manner, cutting down and replanting trees will become a quicker and easier task, as one will no longer have to switch between your chainsaw and a stack of saplings.