In what report section is the subreport located? If you insert a section above it (which can be suppressed), e.g., detail_a, you can place a formula like this in it, where x is the value currently displayed by the sub in the main report:
whileprintingrecords;
shared numbervar x := 0;
In the subreport report footer, add a formula like this:
whileprintingrecords;
shared numbervar x := maximum({table.ID}); //value to display
In the main report, with the sub in detail_b, move your other fields to detail_c, which you can then suppress by using a formula like this:
whileprintingrecords;
shared numbervar x;
x = 0 //note no colon
You can format detail_b to "suppress blank section", and then display the subreport value in detail_c by using:
whileprintingrecords;
shared numbervar x;
-LB