I agree that adding unlit charcoal to the top of dying coals is a wasted effort. So if you don't have a chimney available, to heat them on the side (yes, a spare grill is excellent for this ...) you'll be sunk.
One thing I've made a mistake doing is to load UN-lit charcoal in the bottom of the basket......seems like it should just lite the ones on the bottom fine & continue to extend the burn.....but, it's more likely to go dead or some coals will dud out ...
I've done it that way but it does take longer and they don't get as hot as they should. If a chimney isn't available, I find that a good old fashioned pyramid arrangement gets them going better than if I had them in baskets, gas-assist or not. I realize for the Performer Weber recommends lighting them in baskets for easy movement later.
namtrag: I've seen the same type of lid thermometer (on different grills) display very different behavior. The one on my dad's '06 moves the dial as easily as a Tru-Temp's and will respond off the end of the scale, some 700 degrees. Maybe they were all that way when new-ish, but on my '92 the needle moves very deliberately and seems to max out at "350" no matter what.
So yeah a grate thermometer is a good idea but know that the lid thermos are not only less accurate but can be totally worthless. (Actually any bimetal spring type can be.)