You need to copy a few things over from your working Tiger installation. With all these in place EOModeler starts nicely (at least with MulleEOF) and doesn't complain. I haven't tested it more.
From /System/Library/Frameworks (Tiger) to /Library/Frameworks (Leopard) a different target directory!
- EOModeler.framework
- InterfaceBuilder.framework sic!
- WebKit.framework
- DevToolsIDEServices.framework
- DevToolsRemoteClient.framework
- DevToolsInterface.framework
- DevToolsCore.framework
- DevToolsSupport.framework
IDEServices.framework - JavaKit.framework
- EOModelWizard.framework
- EOSQLExpressionExtensions.framework
- WODevKit.framework
- libEOControlJava.A.dylib
- libEOAccessJava.A.dylib
- libexpressionextensionsjava.dylib
- libEOControlJava.dylib this is a symbolic link to libEOControlJava.A.dylib, so create manually
- libEOAccessJava.dylib this is a symbolic link to libEOAccessJava.A.dylib, so create manually
- libexpressionextensionsjava.dylib this is a symbolic link to libexpressionextensionsjava.dylib, so create manually
- EOMBundles if available
- EOControl.framework
- EOAccess.framework
- EOInterface.framework