Actually, maybe it is possible.
I just checked the code and it should work when the math part is separated by || from the static time part. Also see here: https://www.elastic.co/guide/en/elasticsearch/client/net-api/current/date-math-expressions.html
Example: 2015-05-05T00:00:00||+1d-1m
Kibana doesn’t support the full datemath Elasticsearch does, but from what I can tell this specific thing should work (haven’t tested though). Sorry for my initial misleading answer, I was pretty certain that specific syntax was Elasticsearch only, but I’m not so sure anymore.
Let me know whether it works for your use case.