Ok, it works like this:
you have to specify a file with the filename: projectname.lgp.AssemblyLocations. In that file, you write simple xml where you define the location of an assembly with a given name.
Example:
<assemblyLocations>
<assemblyLocation name="TestConverters, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" filename="..\TypeConvertersTest\TestConverters\bin\Debug\TestConverters.dll"/>
</assemblyLocations>
As you can see, you can specify paths relative to the project file location. Now, at project load, this file is read first. Then the project. It can be that an assembly isn't found during project load, in which case the contents of this file is checked. If a match is found the file is loaded using the filename specified. If the assembly name isn't found the dialog still pops up.
You now can also use the AdditionalTypeConvertersFolder in the project, just leave the type converters there.
So, simple solution to a nagging problem. Hopefully it solves your project load problems. . This is available in the next build, which will be uploaded shortly.