As far as I know, there isn't a way to upload a CSV into a segment, but you don't have to do each item on the same line. There are two different types of comparison operators that you can use - equals any of or contains any of. If you have 200-300 products, you probably wants "equals any of" since you can have up to 500 items per row. In your csv file, put a comma after each item, and then just copy it all and paste it into the single line, the comma will delimit the products for you.
If you want it to be space delimited instead you can use the "contains any of", but that only lets you do 100 per line. You can have more than one line and just use a hit container with an "or" operator if you wanted to do it that way.