How to use more buttons than you have inputs for

With MiniPacs, i-Pac2s, and iPac4s, it was a real hassle to know what the right board was to convert game inputs into something the computer can hear through PS/2 or USB. I've already got my Mini-Pac, so figured I should really nail down what I'm going to use it for. This should also help me deal with my control panel design a bit better.

At this point I want the following
qty | why
---------
8 * | 4/8-way MagStikPlus per player
12 * | 6-buttons per player
2* | P#Start button for each player
2* | coin# for each player
1* | ESC (quit) (to P1btn7)
1* | Tab (Mame config P1btn8)
1* | Pause (Mamewah config P2btn7
??? | Unknown - can always un-double-up something (P2btn8)
1** | 5? (next emu in Mamewah -- shared with Coin1)
1** | 6? (next gamelist in Mamewah -- shared with Coin2)
1* | left-Mouse
1* | right-Mouse
4* | trackball
2* | spinner
3** | 3-buttons for trackball/spinner to use (shared with P1btn1-3)
1** | Start game in Mamewah (shared w/ P1Start)
1** | Menu in mamewah (shared w/ P2Start)
2** | Pinball left/right flipper (shared with P1btn1-2?)
1** | Pinball trigger (shared with P1btn3?)
1** | Coin Door? (shared with Coin1)
--------

KEY:
* = prebuilt input on MiniPac
** = two buttons to same input on MiniPac
*** = two inputs triggered by single button to actuate Shift function on Minipac (YAY I don't have to!)

This should use every input on the Mini-Pac with none to spare. It should only require combining two buttons to a single input 9 times -- a 10th if I actually buy a coin door some day. I think I can handle that.

To explain what is meant by ** and *** I've found some sites that explain these wiring tricks that let you expand on the inputs of your board.

Here's a post that discusses how to wire multiple buttons to share a single input.
The options are very simple to have multiple buttons to the same input (e.g. a coin door and a button both hitting the coin key on a single minipac slot). Just wire them together!

here's a post that discusses how to add more buttons than you have inputs for by having a single button trigger 2 inputs. The Mini-Pac and i-Pac boards from Ultimarc all allow a combination of keys to act as a "shift function", thereby letting you send more keystrokes than there are inputs on the board.

The options are much more challenging to understand if you want to start wiring up a dedicated button that works via the shift function, though they mention $1.50 adapters by RandyT which sound like they take the headache away from wiring n00bs like myself. Of course I could always just design the CP to indicate what happens on a button if you use the shift button manually (hitting 2 buttons yourself at once).