Hmmm... you have a point...

I know... the Balor Bomb!

Time Stop. Gate to Summon a Balor. Have him summon a balor. Etc. So now you've got four or five balors around. Another time stop, rinse wash repeat.

Now, what do you do with ten balors? Easy. make 'em surround the dragon.

Gold dragon is LG, these things are Evil, so Dragon attacks Balors. If they win, fine, summoned critters go where they belong. If the dragon kills one, Death Throws, and you have a chain reaction, multiple balors going off should be able to take the thing down.