Manual code folding can be added by writing your own small Eclipse plug-in. What it take is implementing two classes and packing them into an Eclipse plug-in that registers onto the org.eclipse.jdt.ui.foldingStructureProvider extension-point.
This is probably not the awnser you were hoping from, but as far as I know the only way to add custom code folding to the Eclipse Java editor. From your question I see that you are mostly a visual-studio user and as such not familiar with Eclipse plug-in architecture, but depending on your experience with general plug-in architectures, extending Eclipse is (in small scale) pretty straight forward.