Hi Bellam
As a workaround, you can use PS module for this reason.
You can have WBS structure to represent the IO group. Mark WBS elements as Statistical and Internal orders as real objects through substitutition rules. You can budget at top WBS element level (representing thwe IO Group) and each WBS as the IO within the group. For simplicity, use the naming convention of WBS & IO same. While posting, you need to enter these WBS instead of IO. To avoid the postings directly to IO, you can implement validations too.
Hope it helps
Regards
Mustafa