I haven't implemented any dual-role functionality (yet). I find tapping Backspace an unnecessary exercise, as usually Caps+T+O or holding down Caps+O beats it in efficiency without having to hammer a key with a weak finger. I recommend using Ext+T+O a lot, as deleting and retyping the whole word should help you learn to type the word correctly. It's faster than you think to do it that way, and more productive than repeated backspacing in most cases.
Maybe I should add dual-role keys at some point, but generally I haven't seen the need for them yet.