In an earlier blog post here, Great Maintenance Orgasms, I mentioned and described the Male Clitoris Massage, the original exploration of the fully retracted penis, prior to the self-retracting, using a manual retraction technique.
This is from an earlier introductory post in a thread of mine of mine "Full Penis Retraction for External Prostate Massage":
>>> I occasionally practice full retraction of my penis and fold the bunched up shaft skin at the surface to help restrain my penis from its natural tendency to be stimulated by this and return semi-erect. I lightly carress this folded, now very labial skin, applying a gentle pressure. The subtle movement is a fabulous massage of my prostate! Very slight engorgement of the penis in there just adds "fullness" and a bit more pressure at the prostate.
Makes one reflect on a key fact of our genital anatomy; that our penises are semi-autonomous double-ender "flesh-dildoes" that are perpetually making love to their host.
We are the only species with a non-retracting penis, which has produced myriad cultural responses as to what to do with the thing when not in use! But it still is an inheritance from our penis-retracting ancestors and it can be manually retracted and so used occasionally as yet another enhancement to this aneros practice. <<<
That thread then goes into more anatomical detail and the reports by several other guys of their successes with this technique.