David and KHWOZ are correct -- it would be much more expensive and inefficient to extract liquid molasses from the very diluted dry molasses product, and it would not be particularly easy to get a good yield. If you need liquid molasses, it's best to buy it as liquid (unless of course you have an abundance of inexpensive dry product that you don't know what to do with). If you need a liquid sugar source and can't get liquid molasses, consider sugar, corn syrup, or fruit juice such as watermelon juice, depending of course on what your need is in relation to the dominant type of sugar in the source and the price/availability. For a soporific discourse about molasses, see the discussion on the Livestock and Ranching forum called "Molasses From Feed Store OK?."
If you prefer to avoid the very energy intensive and environmentally damaging commercial sugar production process, you might want to consider making your own sugar for your horticultural applications. The grain/diastase combination that begins the beer brewing process and/or the gasohol ethanol production process are simple places to start. The process's enzyme kinetics escapes my memory at the moment, but there probably is plenty of discussion on the Web if you're interested in that aspect of it.