It can be done thanks to the new LibraryGlobals.
1 Create a new libraryglobal "YourLibraryGlobalName"(choose subtype Drawing symbol/Library Global Settings).
2 Make a parameter for instance BooleanUseOffset, write a UI in the library global.
UI_INFIELD{3} "BooleanUseOffset", 10, 10, 265, 18,
7, "", 2, 1, 0, 0, 0, 0,
1, `Use offset`, 0,
2, `Use offset`, 1
3 Then in the zone you create your offset script.
Before that you write this:
success = LIBRARYGLOBAL ("YourLibraryGlobalName", "BooleanUseOffset", reqBooleanUseOffset)
IF success > 0 AND reqBooleanUseOffset THEN
!here comes your offset script
ENDIF
So now when you set the offset on in the Model View Options Combination you will get the offset, and otherwise the original position. Note that this way you can only modify the offset when it is turned on in the MVOC.