You could create a PROCedure that uses the generation as a symbolic parameter. Then you would only need one set of jcl and as many EXEC statements as was necessary.
As dick scherrer says, your process could be done in one job step without using Rexx, but the JCL would be more complicated than you might want. A Rexx solution as others have proposed is certainly possible, but it would require Rexx programming and it may be more complex than you (or for that matter, the people that have proposed the Rexx solution) would like.