the "straight line" is called "series"
if you hook a capacitor and a LED in series, the light turns fully on, then dims (when the capacitor is fully charged it creates a "pseudo-open" in the circuit, so current can no longer flow). you might use a SPDT switch, with one of the paths through the capacitor, and one of the paths straight to the LED (through a resistor of course) so if you switch it "off" it dims to off, and if you switch it "on" it is simply on.
let me know if that needs clarification.
good luck
david