Tools (SSMS, Agent, Profiler, etc.)
Add an additional type "SQL Server Integration Services Package (32-Bit)" that for 32-bit servers is the same as "SQL Server Integration Services Package". But for 64-bit servers calls the 32-bit version of DTExec.
This would allow the user to continue to use the SSIS features in SQL Agent without losing functionality and should not require much in the way of effort. An additional entry in [msdb].[dbo].[syssubsystems] that contains the data for the sub-system that points at the 32-bit DTExec should be possible.