You can do this using the Job Group imposition in FFCore (part of the OM license).
You can use the following imposition settings
A few things to note - the Guillotine Cut Layout Style will ensure you have clean edge to edge lines to separate the items.
The job group imposition will evaluate the percentage of the press sheet that's not used for imposition. If the amount of waste is above a certain threshold, the imposition will decline to impose the job. You can then evaluate the last imposition preset applied to the job and route the job to another portion of the workflow (either to a different imposition or to a Collect node so the jobs can be ganged up with other jobs).
I did not show the above workflows. Instead I set the waste threshold to 100% to force the imposition to always impose (even in cases like this one which would result in significant waste).
Note - Row and column gutters are applied uniformly because the number of items in the layout is determined on the fly during execution.
Once the imposition is defined, you enable the job group imposition in the workflow itself
To use the ganged imposition the jobs must be part of a job group
I created 3 dummy cards and submitted them to the workflow.
As you can see they were imposed together but the layout does have a significant amount of waste
The Asymmetric imposition will automatically rotate items in order to add as many as possible to the layout.
Alternatively (and if you do not have the OM license), you could use this approach to place each item in the layout: http://forum.support.xerox.com/t5/FreeFlow-Core/How-to-define-watermark-dimensions-using-variables/t...