How do you get the DME from IHZ when you're tuned to IGX?
The only way to do that on the A-320 would be to use the abnormal procedure for loss of both MCDUs and select Back Up tuning on the Radio Management Panel.
Might be being dim, but you'd have the LOC Freq (109.1) auto-tuned in the ILS field, and manually enter the IHZ (109.1) in one or both VOR fields on the RAD NAV page? Then ND displays as required...