You should be able to do the count in the subreport. Once that is done pass the value to a shared variable. Then use the shared variable as the means to display it on the main report.
It might look something like this
subreport - create a new formula
WhilePrintingRecords;
shared numbervar x;
x := 0;
x := Count{datafield name};
x;
New main report formula
WhilePrintingRecords;
shared numbervar x;
x;
The idea is the count occurs while the records are being printed then the main report reads the count. Depending on groupings, etc., you need to keep in mind number of passes CR makes in creating reports and subreports to get the proper placement of the formula.
Hope this helps.
Regards,
John W.