If the players are all '4e style' trying to kill 'em all. Waaaarrrrrrgh! Gently remind them with a soft move on a near hit or missed roll of the impending doom that awaits them if they try to plough through the WHOLE TRIBE. Dangle hints of other things to do or that are more important in front of them.
If the player's go with the strategic plan you outlined they may try, think fictionally of a threat to this, don't worry about the individual HP / Dam of the goblins.
Perhaps your move on a miss is to 'overwhelm with superior numbers', pinning one of the characters down.
Use up their resources other than HP. Take away their stuff (light, weapons, armour, dungeon gear, spell books) on a miss. Give them hard choices on a near miss, or state the consequences and ask them. 'Sure you can perform a sweeping arc attack and slay dozens of gobbos with a whirlwind of death, but you will most certainly sperate yopurself from the others as you dissapear into the mass clot of the melee, leaving yourself cut-off, alone and without the back-up of your party. What do you do?'
Use environmental effects, have the wizard's magic missle set fire to tents, sending billowing, choking smoke into the warrens,
As the Dwarf slices the head off a goblin, have it sail through the air and land at the feet of a terrified child goblin or mother, bawling in fear. The next nearest target is the mother, what do you do?
If say the wizard is casting magic missile and rolls a 7-9 and chooses 'expose myself to danger' then have him sorrounded by a rear guard and threatened with capture (he is a wizard after all!).
Have a wandering band of Icescales stumble into the warren maybe?
Maybe the cleric recieves a vision from their god hinting at the party's deaths at the hands of the goblins / lizardmen, or the awakening of the idol.
You could have a cut scene with a hint of Grundloch up to no good, or the demon pacing his room or the Guaraax swimming about below.
Just remember that although the 'scene' is the encounter of the players with the goblins, there are 'ripples' that spread if they choose to overcome the obstacle with combat. Not the least of which is the reduction of their 'mistake margin' (HP) resource.