Ability to add associative arrays to created nodes

Issue Summary

The module has an existing command to add an indexed array to a new node. However, it would be extremely useful to be able to add an associative array. My case comes from interaction with the OG module, where a new node has to have the group node as a key, not a value, when you create the node. (The OG module converts the group keys in og_groups to values as part of the creation process. This is probably the cause of the various discussion/support requests saying that the command og_groups: [gid] doesn't work.)

Basically, it would be good to have a command that looks like this (if your gid was 206):
og_groups: [206 => 206]

I'm sure there are other uses, but this is probably one of the most common.