Can you give us a bit more information about what you're trying to do with the commits in Pipelines? We have some ideas on this topic (pushes with multiple commits), but would like to understand the problems you're facing first.
I think providing environment variable BITBUCKET_COMMIT_RANGE would solve this this problem. This issue is similar to #15892 in both cases commit range would be a sufficient solution. In my case it would allow rebuilding only changed services in monorepo. Example use was described here: ci/cd of microservices using mono repos