Oh man, I have been there several times! It's been a while since that has happened to me, but it used to all the time.
My way of avoiding that now for the most part is going into a custom figure without
a plan. I just rummage through my custom fodder boxes, looking for interesting parts that might fit together, might not. I rarely, if ever, have much of a concept of a figure planned out. Maybe the head or the torso might be my starting place that I am thinking of for a figure... but other than that, I just kind of "let it happen."
I can't wait to see what you come up with though for this month's challenge.