As suggested above, if you are able to define the criteria for your filter, it should be relatively simple to create some session relevance that would identify the desired Fixlets via the REST API. You can then use that as input in a sense to automate the creation of a baseline via the REST API. So, what are the filter conditions/criteria?
All that said, have you explored Patch Policies? Depending on what you are trying to achieve, it may help provide similar (or better) functionality.