What you want is an "Open jaw". The trouble is if the airlines will sell you such a ticket for that gap. You'll have to check for airlines that fly between BOM and both AKL and HNL (or at least use codeshares to get there) to try to get a cheap excursion ticket (that'd rule out SQ, MH and CX off the top of my head). I'd look at CI, QF, PR, KE, JL, NH to start with.

If you plan to use an online reservation system to check fares, just use multiple destination and specifiy BOM-AKL as one leg and HNL-BOM as the 2nd.

You might also check for BOM-AKL and BOM-HNL r/t and get a OW or throwaway r/t HNL-AKL and see if this combo is cheaper.