Maybe this is what you’re looking for: Easy sending some XML with MKNetworkKit.

This works for me:
MKNetworkOperation *op = [self operationWithPath:@”api/0.6/changeset/create” params: nil httpMethod:@”PUT”];
[op setCustomPostDataEncodingHandler: ^NSString *(NSDictionary *aD){return @”Put your XML here“;} forType:@”text/xml”];

That’s it