Try to create setup.ini next to setup.exe and insert something like that
Code:
[ExtractSettings]
FreeArcFile1=Data1.cab;DestDir:{app};Disk:1;
FreeArcFile2=Data2.cab;DestDir:{app};Disk:1;
FreeArcFile3=Data3.cab;DestDir:{app};Disk:2;
And so on.
Of course set "Disk:#" corresponding to your "Data#.cab" placement