The phrase "additional excuse for" is correct and usable in written English.
It can be used when discussing reasons or justifications that supplement an existing excuse or rationale.
Example: "He provided an additional excuse for his tardiness, claiming that traffic was worse than usual."
Alternatives: "further justification for" or "extra reason for".
According to Politico, the politics of the announcement provided an additional excuse for networks that didn't want to see their ratings deflate on Thursday.
No one protests in empty places; and if hobos and dealers contribute to make the area still more uninhabitable, it will constitute a good additional excuse for a real estate company to decide its redevelopment someday (in the same way as the Renaissance Center wants to do for the Downtown, serving as a point of attraction for tourists and casino gamblers).
Preventive psychiatry is a bad idea in the best of hands, it can be a menace in the worst -- an additional excuse for furthering the current practice of wanton overmedication.
If anything, the media's current obsession with Donald Trump ― his every utterance or tweet treated as "breaking news!" ― just provides one additional excuse for highlighting trivia, while slighting issues that deserve far more attention than they currently receive. .
Supporters of the Disclose Act did not help their case by adding several extraneous provisions that gave Republicans additional excuses for voting no.
And really any excuse for additional Tolkien geekery has me on board.
New York City's public schools may be in need of additional funds, but that is no excuse for the city's children to leave the system lacking a basic education.
People no longer see racism--personal, institutional or otherwise as an excuse for underachievement, a rationale for special consideration, or a basis for additional societal support.
— are no excuse for inaction.
A convenient excuse for philandering?
