You don't need CO2 for lush growth. Excel is not fertilizer but a source of organic carbon. Try using root tabs. Just place them deep into the substrate, and watch your plants grow. Replace every 3-4 months or if your plants start to turn yellow/stop growing.
There are plenty of low-tech, planted tanks on the forum. Here's some great examples:
Low Tech Tank Show-and-Tell (low tech can be lush, too! =)
And here's a nice looking african clawed frog tank:
Have you got herps? Show em!