What, if you have buy trade to place it's stop at the lowest price since the trade was created? I think I'm missing something, because doing this is basically closing the trade right from the beginning or pushing SL further and further so it can't be reached (at least until the EA is removed).
If you want to place SL to the lowest value back in the history (for some time), then something like this: http://prntscr.com/4c34n8