Discharge / Bleeder resistors
Because the residual charge would be DC, anything on the 120V AC mains side of the xfmr can't very well bleed it. However, if a slight loss of efficiency if acceptable, you could place a 1Mohm to 1.2Mohm resistor from L to G on your output. it would only bleed about 1-1.2mA of current (about 1.2-1.5W) during operation, but your 5-10 minute "powerdown time" gives 300-600 seconds for that "trickle" resistor to discharge the line significantly.
Alternatively, if you can source/afford/build an inductor with a similar resistance at your AC frequency, your efficiency loss would be similarly minimal (attaching the inductor from L to N, same as resistor), but would appear as nearly a "dead short" to 5he stored, capacitive DC charge, and most likely discharge the capacitance below 1V in >0.25sec after mains input power is cut.