Any special or home-made tools you use?

What I do is go from the opposite way.  For instance if I am glueing the top, I put the clamps from bottom, especially the spring clamps HF because the pads actually have a little bit of movement and it helps create a tighter clamp.  One of the things I do for wings is I have a scrap piece of wood with a 45 V groove in it for putting in a set of C clamps.  

What about good old rubber bands?

I use those metal binder clips of various sizes. LOL! I swipe a few from my office.

Not completely home made; but I use the draw string you find on sports gear and jackets and hoods. I use old ones to hold something larger (ex; submarine halves) together that don't require a lot of pressure. The small plastic slider locks the elastic string/cord in place quite well.

I just hold 'em with my hands until the glue sets.  Doesn't take too long with solvents like Tamiya Thin.

Some things you just can't clamp.  I understand your problem.