I was kind of bored so I threw together this bar-graph board that fits right on top of the Pro Trinket footprint:
As you can see it's made of a SOIC-16 breakout, some 0603 LEDs and 0805 resistors. It's a tight fit but the LEDs lined up good enough to not get shorts in between. And well... you also see what I had to do to make the resistors fit :)
Unfortunately there are no 8 I/O pins right next to each other. Since the Aref pin is between D13 and A0/D14 I had to connect the LED that lines up with Aref with a wire.
All of that just for some lame gif:
Sorry for the bad camera work ;)