However the PAPI is useless if in IMC.
True. If you're on an NPA to a displaced threshold with a temporary PAPI and your state authority does not allow you to create your own profiles (you certainly can't do that in Australia) then all you need to do is adjust the chart profile by the displaced threshold amount (320ft/nm) and do the approach in VS or FPA, down your profile.
Alternatively, VS or FPA down using the VDEV bar but sit for example 50-100ft above it depending on the amount of the displaced threshold (I'm in a Boeing but sounds similar to yours).
You should keep a practical mind to all of this though; deliberately popping out low on the PAPI isn't a big issue; raise the nose a bit and fly into the proper slope.
If this
is a big issue, then your company Flt Ops management should have issued guidance on how to tackle the problem eg raise the MDA so that you have enough time to pop out low on the PAPI (after following the database profile) and correct back to on-slope by 500ft.