[ovirt-users] [ovirt-engine-api-model] Any solutions to add custom key/value pairs into entities?

Hi all, In my case, I need to add customized KVs into API model entities, such as VM, Disk, Template and etc. I looked through the API model documents and got some existing Tag/Property/CustomProperty structs, all of which have limitations and can not work it out. Are there any solutions? Thanks, Joey