Heh, I compared the two side by side. The casting is the same. It indeed looks possible if the inner static lens and the bottom knob are removed from the Parnel. To do this, you would have to completely disassemble the fixture. The lenscarrier on the par has the same teeth that the knob on the Parnel drives.
If you needed an extra par or two and had extra par lenses then I suppose it might be worth it although it would be a labor intensive procedure to complete and restore.
I have done this conversion in the opposite direction (Par to Parnel). The basic shells are identical castings and with the assembly manuals from ETC for both models you'd be able to determine what parts you'd need. I ordered all the parts via Full Compass.
Personally I wouldn't bother, especially if you have to buy the parts to convert. If you keep an eye on eBay it's not hard to find pars for $40-$50. So just buy more pars, or sell the parnels and use that money for pars.