Well you can make a simulation of an impalement, its not that dangerous, you just need to find the right person, ofcourse you dont need to impale or get impaled farther than a usual cock... Just use a dildo not a stake, if you want to make it looks more realistic attach a dildo on a javelin, this can work easily even if you are completely amateur, tha same with a crucifixion you can use ropes instead of nails, but try to buy a cross not build one yourself and ofcourse try not to fall and don't bind the ropes very tightly, that could stop the blood circulation i guess... But the most difficult part of doing all of the above, as i said is to find the right, willing person.