Crystal Reports Shared Variables and Report Selection

Message

   Morning All, I have setup a report using Crystal Reports 9 which contains a main report and approx 9 subreports.  So far so good.  The main report and subreports all use the "currentdate" as part of the Record Selection, also so far so good.  Occasionally when there is a bank holiday for example I need to run the report on the day of return for the previous days, so I have been amending the "currentdate" to "Currentdate -x" etc etc however I need to do this on all subreports.  I thought it would be better to setup a shared variable which I could assign the "Currentdate - x" and reference in the subreports and cutting down on the amount of changes I need to do. 

That's the background now the problem:- I can't seem to get the created shared Variable to be used in the Record Selection of the reports or subreports, is there a way I can do this or another way to achieve my goal please.