Edit: Sorry this ended up a rather long post

I'll leave the how-too's to more knowledgeable people. if you do want to level your pala as one of your dual-box group you can always have it helping your other dude level up.

I have a priest and warrior who are now almost at the same point, what I've done up until this point is use my priest just for healing, to minimise my warriors downtime.

The priest isn't grouped with the warrior (as this would reduce xp gain).

If you wanted to do this for your pala what you'd need is a targeting macro with your mains name (rather than a party number, as you won't be grouped).

Then stick your healing spells on a button (probably worth downranking as it's not worth healing your toon for 1k if they only have 300hp)

Stick your buffs on a different button (so wisdom for casters, might for melee).

Then Seal of light, wisdom, justice on another button and Judgement on the last.

For the judgement one you probably want a macro that reads along the lines of:

/assist <main's name>
/cast [harm] Judgement
/stopattack
/target <main's name>

Fairly simple, but basically it will judge whatever your main is fighting with whichever seal you have up and then retarget your main (so you can carry on healing. The /stopattack is to prevent your pala one-shotting the mob if it's in melee range (never used it, so apologies if my wording is wrong).

So you can use light for melee toons, wisdom for casters and justice to stop the mobs running off and agroing other groups.

So your pala can turn into a nice support bot while your secondary class levels up to the same level.