Ok let me answer this myself
Apparently IT IS possible to add custom data sources in cacti 1.0.x , following this post
and modifying the following setting:
Seems you can create data source independently:
Settings->Other Settings->Graph/Data Source Creation Method = Advanced
The default is "Simple" which disables this functionality.
Now anyway, question still remains that possibly it may be much more clean to be able to create a graph template that calls back for a multiple SNMP get data inputs with manual insertions OIDs.
Is this something possilbe? (feature request?)