A focus based system makes this very easy to do, give each pally a 'buff' macro like this and bind it to a key/bar:

/cast [target=focustarget] SPELL

Then using your main, select the target and press the key, bingo each pally casts their buff on that person. Takes 5 clicks and 5 key presses to buff the whole party and is good for buffing passersby too.

There's link in my siug for setting up a simple focus based system.