Gilgit-Balistan is the only region in the whole of Pakistan where Sunnis are a minority. 40% are Shia, 24% Ismaili (a sub-sect of Shia), 30% Sunni. There were even less Sunnis there until Gen Zia ul-Haq started encouraging migration of Sunnis from other areas. So even he knew that was their weak point.

Apart from migration, Gen Zia's ordered 1988 massacre in response to the civilians in Gilti who revolted against him. Shias and Sunnis have a long history of sectarian violence in the Pakistan.

The only way we can liberate Gilgit-Balistan is by providing weapons and training to the Shias there. The seeds of hate have already been sowed by the Sunnis there.

Later, they may or may not join India. Even if they don't, they'll be helpful in keeping the rest of Pakistan or the Punjab province (if Sindh, Baluchistan, NWFP have been liberated) in check.