Graph prototype for more than one LLD item

I need to build a graph prototype that could include more than one item prototype in comparison with an static item.

For example: I have an item that grabs the result of ulimit -n, wich displays the max open fds that a process opened by the user who invoking the ulimit command could open. After that, I have built a simple shell script that counts all opened file descriptors of the processes that I want to monitor. This script is used in conjunction with a discovery rule that gets the name + the PIDs of the processes, assuming this name convention: processname(pid), to make unique item names.

My goal is to display a graph which contains all file descriptors opened by the monitored processes in comparison with the result of uname -n.
When I have created the graph prototype with this name: 'Number of open file descriptors by process', the bellow error was displayed in the next loop of discovery rule:

'Cannot create graph: graph with the same name "Number of open file descriptors by process" already exists.

After changed the graph prototype name to "Number of file descriptors used by {#PROC_NAME}", the error wasn't displayed anymore and the graph could be created. But it was created with the unique LLD item name. So, for each monitored process, there will be a new graph. This is not what I want.