An easy way around the problem is to load up on cheap, fast growing stem plants to fill in the empty spots, then remove them as you fill in with the plants you really want. Floaters or plants that do well left floating are potential options as well. In my tanks that's generally excess vals, stargrass and hygro cuttings--plants that are forever in need of thinning.
If you don't have existing tanks to pull from, look for packs of very common stems for sale; the stuff that everyone has and grows so easily that folks sell it in very generous portions. I've gotten some really nice cuttings packs here, for example, for little more than the cost of shipping.