Anyone know if a reservoir can be added after the fact?
Yeah,
got take it apart though,
the ''floater piston'' (seperating oil from gas) is in the top of the can.
it will need to be moved to the reservoir.
If you are talking Emulsion shock, there is NO IFP in the shock can. Hence, an Emulsion shock. Easy to do, you must order the correct hose though. "Old'' style has the Schrader valve threaded into the can. 'New' style, the Schrader has an O ring. FOX has a hose for both. IFP is in the reservoir .