You can redeem miles to anywhere in the overall network (in theory - rumour on here is HNL is impossible to find availability for!). However, MFUs can only be applied to wholly BA-operated itineraries. This means you can fly with an MFU to SFO/LAX/BOS as
Swanhunter suggests but have to make your own way to HNL (e.g. on AA), on a separate ticket. Paging
flyclub and/or
BA97.com for tales of their YUPs out that way
Phil