From: Mega Mana | #256
You'd rather have Kanon coming in, taking Battler's place in the closet, and then switching personalities/giving up Kanon's personality as a solution and an acceptable dodge around the red truths (with it all coming undone as soon as Erika opens the door and sees who is inside), than an acceptable and inventive way to exit the room that has many hints laid out all through the chapter?
Kind of late to the party, but oh well. Anyways, to this I'd have to answer yes.
An answer supported by hints laid out throughout the chapter, as you say, would ruin the point of this particular closed room. Ryuukishi purposely made it impossible to solve if you just looked for hints in the scenes directly related to the closed room, and instead made it important to pay attention to the parts about romance and love. His purpose in writing Umineko was to create a mystery that could only be solved with both logic and emotion. The theme of the entire series is without love it cannot be seen, and the finale of EP6 perfectly embodies that theme.
On another topic, George, Jessica & Nanjo's murders in EP3 are not covered by Will and Clair in EP7. I wonder if you can solve them now?