Appending to a file is a fundamental feature even in software in lower levels of the software stack like the operating system routinely perform. This thread has been active over 4 years and the need for the feature will not go away. On the contrary, the need will increase as Evernote is integrated with more research, authoring and knowledge storage applications and workflows.
As the head of software engineering group, I respectfully think this feature merits some updated official acknowledgment as to when it will be on the roadmap, a legitimate automated workaround or a reason why it can't be done. A lot has probably changed in the source code for Evernote and the Web Clipper since the first official response. The complexity of this feature can be greatly reduced by simply manually selecting which note to append to first and then building from there. If is it is really that expensive then make it a pro feature.