wagonR Duo pathetic mileage

I have bought 2nd hand wagonR Duo (June 2008) LXI (Company fitted LPG) Over all riding experience is excellent it's very comfortable and spacious. In the boot space they have given a stand for spare wheel which occupy half of the boot. LPG tank is hidden in the boot that not a problem. Main problem is in LPG with 80% AC I get mileage of 8.5 - 9. I traveled 245 Kms and for that I needed 40 ltr of LPG and it's very tough to find LPG filling station. Does converting LPG to CNG will be helpful? Will mileage in CNG increase??