Yea, 30" tall tanks are tough to work on and as you've found out most the work is at substrate level. From your pic it looks like you dont have much depth in your substrate, you could add more so you can reach the bottom a little easier.
Check out Leopard Vallesneria. They definately will fill a portion of your tank and look nice; they'll fit with your current scape too. Of course stem plants but youll need high light and CO2; with a tank that size you could try high light over just a section. Either way, you have to fertilize or you're not going to get much growth.