This is an idea I implemented on my '88 runner, building off of what 4crawler has on his website, and an idea from Big Ern on Pirate BB. It seems to work, no problems as of yet.
I sort of combined the idea of adding a relay to take a load off the ignition switch and powering the coil in the starter from the battery directly. Mine has a starter relay already, but instead of just running power straight from the battery through the contact of the factory starter relay to the coil of the relay in the starter, I added another relay. Using the one wire coming from the ignition switch that used to feed power through the factory relay contacts the the starter's relay, it now feeds power to a coil of a second relay, and then the contacts that close send power directly from the battery to the contacts on the factory relay. So this drops the amount of current that is going through the ignition switch, and also eliminates the problem of a stuck relay if you just wire it directly to the battery.
Here is a diagram:

 

Looks good, pretty much the idea of the Painless HotShot relay aside from the location. For that relay, you just add it right down at the starter and just route the solenoid wire up to the new relay and the output of that relay back down to the starter. But anything to take that ~20 amp solenoid load off of the ignition switch is a good idea.

 

So, the older trucks don't have a starter relay?

 

Nope, I think those came into play around 1986 on the manual transmission trucks. All tied into the clutch cancel switch which is also not present on the older trucks. Also, the automatics do not have a starter relay either, only the neutral start switch.