[galaxy-user] Filter fastq by percentage of ambiguous (N) bases

Hello, I like to filter my fastq files (50 bp single end Illumina RNA seq reads) by a maximum threshold (10%) of ambiguous (N) bases. I can see that the "CLIP" tool removes all reads with one or more N bases. Is there a way to remove only the reads with five or more N bases using Galaxy? Thank you. Best wishes, Anto