Create something like http://builder.seaside.st/ but for building your own Smalltalk images, using Metacello and Loader. This should work at least for the Smalltalk dialects that supports Metacello and Monticello. In that website you should be able to search projects (Metacello configurations), add/remove them from your list, select a particular version, look the project description, authors, releases, etc. Once you have finished selecting all you want, you can download a script to run in your image or the server can even create the image for you and give you a link to just download the image.
In a further step (probably even optional and a bonus), it would be nice to create and compile your own VM using VMMaker. This would be like a web version of VMMakerTool, where you can select which plugins to compile and if you want them internal or external. Then, the server should be able to automatically generate the C code and build the VM for you. The main problem is how to build the VM for different OS when the server is running in only one in particular. Another problem would be that the VM code has some strange dependencies that should be fixed.
Finally, this bonus is important to spread the "build your own vm". This would help people to know how to create their own VMs, have less fear about it and not depend on VM gurus.