I picked up a true Bally pinball plunger off ebay for about 12$ a while back, really simple to install, and just made a little bracket for a standard cherry switch (although I ended up using a Roller switch from Happ).
Kinda nice since externally it's all metal. I think I'm going to have it brass plated to match the rest of my CP.
But really, setting it up wasn't tough at all.
I just set my WinIPAC so that the plunger is the ENTER key. and set the cherry switch such that when the plunger is just sitting there, the switch is depressed.
Then Wire up the NC connection of the switch to the IPAC (this is backwards from normal pushbuttons, you wire then up to the NO connection on the switch).
That way, when the plunger is sitting there, the switch is pressed in, but there's no connection made.
When you pull back on the plunger, the switch is released, and the NC connection makes contact, and you get an ENTER button press.
What's cool, is the farther you pull back, the longer the enter key is pressed, which for most pinball games controls how far back you pull the plunger.
It's not 100% accurate, obviously, but it works close enough that most people don't notice.