I don't have a "real" solution for that, only an (ugly) suggestion how to cope with this problem in general (nevertheless it's nothing but a workaround, no discussion):
After having created all the workflows from the TDM plans, don't run the plans immediately.
Instead, export all those workflows to one XML file; use an automatic process to replace the cache size 8MB for sorter transformations by Auto (or by a value which you consider suitable for your machines); re-import and re-validate these workflows; and then only run the workflows.
Of course that means you will have to repeat this process every time the plans are changed. But at least this approach can be fully automated, so you have a workaround which is at least easy to execute (instead of executing any manual work).