I suppose a cheap way of handling this (if you have a few basic electrical assembly skills) would be to rig up a board with a lamp socket in series with one of the conductors of an extension cord. You could start with this in circuit and power up with a 7 or 15 watt incandescent bulb, then power down and go to a 40 w, then a 100 w bulb. That should pre-condition the caps. I guess if you wanted to get fancy, you could use a dimmer switch in series with the bulb.
That's what I would do considering I don't have, nor do I have access to, a variac.