This is a situation I've found myself in many times
My record is 26 (yes, you read that right, twenty-six!) pinhole patches in a LE bladder - a friend of mine crashed their kite into a gorse bush, which has thousands of nasty little needle-like thorns. Anyway I have found the best way to do this is to remove the bladder, close off the one-pump valves etc., and pump it up as hard as you dare. Then get a bowl of soapy water (you won't need much), and wet your hand with it. Slowly run your hand over the entire surface of the bladder, dipping your hand back into the soapy water frequently. What you're looking for is the tell-tale 'feeling' of the air bubbling out of a pinhole under your hand. You will be amazed how sensitive your hands are at detecting the tiniest of leaks. When you find a leak, dry the area and mark it with a sharpie. Then carry on and inspect the entire thing in case you find more.
This process can take a long time, but some benefits of my technique:
1. You can do it while on the sofa with Netflix or something to keep you entertained
2. You don't need to break into the kiddies playground and wrestle with your bladder in the paddling pool
3. No tools except a bowl of soapy water and sharpie marker
Good luck! (Actually I've just noticed the date of the post, you've probably already fixed it, or given up and bought a new bladder already!)