Depending on the fruit, you may find the syrup without sweeteners to be too tart.
I don't think adding pectin is the answer. You want a syrup to have concentrated flavors. If you just combine juice and pectin, the best you could hope for is thick juice, not syrup.
I guess you could boil down tons of fruit to get a syruppy liquid but you may not find it as sweet as you like.
"If you want to make an apple pie from scratch, you must first create the universe." -Carl Sagan