graph prototype in LLD: "different {#FSNAME}'s same vfs.fs.size" in one graph

I have this new feature firstly in this situation:
To monitor CouchBase, I use LLD to auto create items for different BUCKET.
One item is BUCKET's memUsed. I have completed that using LLD to create items automaticly when I add or delete bucket.
In graph prototype, I need this feature: to create graph that all bucket's same item(such as 'memUsed') is in one graph automaticly.
But, now, in Zabbix, it can only create graph that one bucket's different item in in one graph. For example, it has no use to put bucket's memUsed,ServerList in one graph.

If you don't know CouchBase, image this by using the example in office document https://www.zabbix.com/documentation/3.0/manual/discovery/low_level_discovery :
put different {#FSNAME}'s same item(Free disk usage) in one graph.