THere's no built in options for sub summary parts that make this possible. Have wanted that feature for years but it's not something the powers that be have ever added to fileMaker.
I won't say that it's impossible, but doing so would be very complicated to pull off.
I was pretty sure that repeating a Sub-summary was not likely since there doesn't appear to any properties which would facilitate this.
Hope TPTB read the posts on this forum for features we'de like to see as part of FileMaker.