Hi Gary,
I'm afraid you cannot evaluate a custom launch condition before the
Pre-Install prerequisite.
When the
Check predefined launch conditions before searching for prerequisites option from the
prerequisites page is enabled, only the predefined launch conditions that are specified in
Software Launch Conditions Tab page will be checked by the EXE setup before the prerequisites are launched.
If any of these conditional statements fail, an error message is displayed to the user and the installation is terminated. You can take a look on the
Standard Action article.
I'm afraid there is no workaround.
If you have other questions, please let us know.
Best regards,
Dan