An old trick for the non-greasable balljoints, was to drill and tap
a small hole so you can screw in a Zerk fitting.

This might be an easy solution if you really want to
keep up regular maintainance.

Start with a center punch and put a dimple where you are going
to drill so the drill bit won't "walk". Use a small drill bit, like about
1/8" or so, just to get a small hole started, drill carfully, use grease
to catch metal chips and keep the bit lubed, there is a small pocket
in the balljoint to hold grease, this is where you want to make the hole.

I would drill the hole at the rear of the joint so rocks can't knock
the Zerk off. The Balljoint on the Sidekick has a sort of round
pyramid shape with a flat top, closer to the top should be where
the grease pocket is, so drill close to the top but still on the angle
so you can get at it with the grease gun.

now enlarge the hole to the proper size as the tap for the
Zerk threads you are going to use. Use grease again to catch the
metal chips, and don't drill deep, just through the outer case.

Now tap the hole, use grease again to catch metal chips,
install your Zerk and grease away, your Balljoints should last
for a long time now.

Darrin