Alberto: Yeap I'm not saying they are sterling examples of Aikido but I found it difficult to find any high levels demonstrating this technique but I may have struck gold:
Watch this one where Gozo Shioda does it and I don't see any use of the leg trip/position. That being said it does look like the uke is flinging himself (though with someone as bad-ass as Shioda one can hardly blame the uke).
But what is more telling is that udekimenage is known as 'hijiate' in Yoshinkan which if I understand correctly is translated as 'strike to elbow?' If so we can safely conclude that this technique as originally designed was to break/strike the extended elbow rather than throw itself and that the dojo version of this technique is just for safety rather than it being an effective technique in its dojo form.
These techniques really should come with an instruction manual :/
Appreciate anyone in the Yoshinkan school to comment on this also