Possible yes, practical no. Effectively you would need to build a new sub-continant to have an appreciable impact on sea level. That said, you don't need to dredge from the low point in the ocean, all that matters is displacing solid material from below sea level to above sea level, so the best option would be to find a shallow sea with an existing archipelago of islands and build up from there making it a deep sea with the islands connected as a continent. Alternately you could go after reefs, despite the collateral damage, with the great barrier reef being the obvious choice, essentially pump up dredged sand from the surrounding ocean bed onto the reef to make new land, the reef has the advantage of being very shallow and stabilized with lots of surface area, so good for making lots of land if you don't mind being the architect of an ecological apocalypse of unprecedented proportions.