Would love to and have already thought about doing just that. Then when I tried putting the full size tire in the hole, it created a huge bump in my trunk which quite frankly is unacceptable as I use my trunk all the time, but only need a spare - - sparingly.
I have since found out some interesting information that I want to share that may help both me and others.
1) The spare tire in my 1995 car came out of some 1999 make/model car. I know this because the JY that sold it put 99 (in white grease pencil) on it. Now I know that only 95 and very very early 96 cars had the 4 bolt rims, so this compact spare came from some other car - most likely a foreign one as they still use the 4x100 pattern.
2) The compact spare for my car is actually a 14" rim. The tire size is T155/70 R14. I have searched for that tire size and found that the Saturn Ion from 2003-2007 used that spare tire size and rim size. Now I don't know if that tire will work yet, but I plan on finding out.
3) The old Dodge Omni (which is really a US version of a Volkswagon Rabbit and in fact used the same Rabbit engine for several years) and its Plymouth cousin (the Horizon) used the same 4x100 bolt pattern, so I wonder if the compact spare for that car may be a substitute, but wow, those cars are probably hard as heck to find now.
4) Many Toyotas, Nissans, and even Hondas, still use the 4x100 bolt pattern, so I also wonder just how many of those may be OK to use.
I understand that the problem is not finding a 14" 4x100 compact spare tire, but it is finding one that will not be a problem using on my car - such that the brakes (front or rear) or steering/suspension components do not come in contact with the rim or tire itself.
I am betting that if I find a 14" CST that has the same T155/70R14 size, most of them would work just fine. I know there is a 1999 make/model car out there that does have a compatible compact rim/tire and when I find it, I'll make sure to tell ya'll.