With our current architecture, this requirement is only possible by using the QueryCellInfo event handler. But as we are currently facing issues when using QueryCellInfo along with CustomFormat. We have already logged an improvement for this and this has been fixed internally.
In our upcoming Volume 4, 2019 release which is expected to be rolled out on or before December 17, 2019, we have deprecated the CustomFormat property and the customizing of European format(or other formats) can be done with the Format property itself.
Until then we appreciate your patience.