Operations/Actions which fire once and receive all objects as a parameter

I suggest writing a node operation. The nice thing about them is that they expect an array of nodes. Your implementation is free to iterate on each or to perform a single action using the whole array.

That's a good idea. But I found another problem: the code in VBO 6.x calls the operation repeatedly with a single node, even if it's a node operation. I did this to simplify dealing with Batch API. I'm currently working on making node_operations accept arrays of nids, and I'll add a way to specify node_operations forms, just like actions.

OK. So the code for this is committed to the latest dev. You basically need to implement a node_operation, but with a few twists:

* In the array returned by your hook_node_operations(), add an attribute 'configurable' => true.
* Implement [node_operation_callback]_form, _validate and _submit, exactly like you would if you were implementing a configurable action.
* Your form elements will be passed to your node_operation callback, in the second parameter.
* The callback will only be called once with all selected nodes. Note that this will only occur if the Batch API option is *not* chosen.

That's it! Please try it and let me know.

Basically, I want to come up with the simplest hack to support your need. Creating hook_comment_operations() would not generalize well to other object types in the future, because I'd modify VBO to support such hooks for every desired type, whereas currently the actions framework can be extended to any object type.

As an alternative, I am thinking of adding an option to the view settings that instructs VBO to call the action once, stuffing the selected nodes/objects into an array that it passes as the first argument. Would that work for you?

It's in HEAD :-)

To use it, just declare an action with new attribute 'aggregate' => TRUE. VBO will call this action with an array of object ids as first parameter. I tested it with nodes only, but it should work for comments... Caveat: custom actions (the ones whose parameters are pre-saved in the database) will not currently work. They will require further hacking.

Theming is a pain! Sorry I couldn't help you.

This introduced a php notice which I've fixed (along with another php notice and a few whitespace issues).

Fixed. Thanks for the patch.

Is it possible to make configurable node operations show up as advanced actions on the actions page to make it possible to make new node operations based on a configurable node operation?

No, that's not an option without serious hacking in the action infrastructure.

However, if you're looking for aggregate actions that are configurable, it is now (6.x-1.7) possible to write your own action that has an attribute aggregate. This action will receive an array of all selected nodes/objects in its $object argument. If also marked as configurable, you should be able to make an advanced action out of it.

Thanks! Exactly what I needed. Works great!