please try it as mulch, dont till it in the soil, just mulch. people will tell you it will make your soil acidic, but please try, and share. I am 99% certain that it will be fine.
I have a LOT of experience composting pine needles, the bottom line is this.
If there are the "waxy" kind?
they are indeed acidic, not to mention it takes a LONG time to break them down.
If they are redwood needles then they are good to use rather quickly, about the same as leaves.
the composting procedure, depending on the other inputs can easily counter any acidity though, just the waxy needles take like 12 months or so to breakdown.
--edit--
you did mention that they are already rotting, if so you could use them already, but the caveat being is ONLY if they are WELL rotten, in my mind that means that you can't visually discern what it is.