Drain via backwash

I'm going to eventually need to drain 1/2 my pool in order to bring my calcium levels down. I was wondering if I could just drain via backwashing (DE). I'm hesitant since the manual says not to run the filter without DE for more than 5 minutes, and I'm not sure if backwashing is considered the same as if it were filtering. I don't have a bypass valve, just filter/backwash.

Thanks...

Any way you can disconnect the inlet to the filter from the pump and just use the pump to get rid of the water?

There are some chemicals that will drop out the calcium as a solid and all you have to do is vac to waste. (TSP or Hydroquest, i believe)
If you had a sand filter, you can also use Zeolite/zeobrite instead of sand, it actually grabs the calcium in a bond, like a softener would, you can then add salt to your filter (system off of course) and let that sit for a bit, then backwash and the calcium will get washed out.