How to insert SPARQL data with POST request body in Blazegraph?

Question

I'm using Blazegraph as my RDF store. I'm trying to insert data in the following format:

INSERT DATA {
     <http://www.test.com/1> <http://www.test.com/2> <http://www.test.com/3> .
     ...
}

Now, if I use the URL update parameter like http://localhost:9999/bigdata/sparql?update=QUERY it works just fine, but the problem is that when the data is too long it will exceed the allowed length of the URI.

So is there a way to execute this same query but sending it in the request body?

I tried just doing a post request to http://localhost:9999/bigdata/sparql with the query as request body but I get a syntax error from the server saying it doesn't expect INSERT, but rather a SELECT, DESCRIBE or other statements. I guess it is not understanding correctly that I'm trying to do an INSERT and maybe I need to send some additional headers/paramters to signal that.