It may pay to find out _why_ isolated ground receptacles are required. Often times there is no good reason for the isolated ground receptacles other than someone thought 'computer needs it'.
For me it is usually 'because the engineer said so'.
Could you run a separate 1" conduit to a panel simply for quiet ground use?
No, the NEC requires the that EGCs (including IGs) run with the circuit conductors.
This is a interesting question and IMO the answer is the following.
The IGs will be required in each of the parallel conduits but they need no be larger than 250.122 requires for any of the outlets served by the IG.
In my experience none of the IG receptacles will be larger than 20 amps meaning a 12 AWG in each conduit back to the MDP will sufficient.
Of course than we run into 250.122(B) which may require the 20 amp IGs to be 300 kcmil as are the phase conductors.