What do you mean by "download selected individual reads"? How do you know which reads you want to download?
fastq-dump allows streaming the output, so you can combine it with
head to download the first whatever number of reads you want. However, there is random access to these files, so you can't access "individual" reads, and there is no way of skipping download a certain number of reads - you can combine
tail, for example, but you still have to download the reads before discarding them.