G'day SRS,
I haven't been there for a while but try this if your FMC will do it,
For RW13L build a waypoint by entering 'IRTH315/CRI041' in the LEGS page and that should generate a waypoint at the intersection of the extended centreline of 13L and the 041 radial out of CRI.
For RW13R try this 'IMOH315/CRI041' and you should get a similar intersection.
Join the legs up and you should have something to work with. The intersection has to be generated using two navaids it won't work if yoy try using two waypoints.
In each case look at the distance from the intersection point to the runway and enter a suitable 'SPD/ALT' (300ft/ml) and you should get a LNAV track and a useable VNAV path.
The only problem I can see is the 13L approach turns inside your generated waypoint but the 13R approach should work OK.
I'd be interested to see how this works.
Of course you could bribe wiggy for his overlay plates!
Regards,
BH.