It's a challenging question because achieving perfection in revolution 5 without using a background image beneath the text seems nearly impossible.
The best approach would be to utilize a static/global layer for the bottom layer, but revolution 5 has a tendency to override z-index and other styling properties, always forcing the layer to display on top. Unfortunately, there doesn't seem to be a solution here.
Another option is to place the layer on every slide in the same position and disable all animations, making it appear static on each slide. However, even if you disable animations, revolution 5 still utilizes animation speed parameters, causing the layer to flicker. If you set the speed to 0, the layer vanishes inexplicably.
The only workaround I can suggest is to manipulate the settings in a way that may not be perfect but could be deemed acceptable. For the bottom (static) layer, select No-Animation and No-Out Animation under the Animation menu. Adjust the animation speeds to 100 for in animation and 1000 for out animation. This will create a continuous appearance without flickering, although there may still be some slight flicker present.
Experiment with fade-in effects and varying animation speeds, ensuring that the out animation duration allows for the next slide's in animation to smoothly transition. It's not an ideal solution, but it might achieve the desired effect.
I hope this advice proves useful, and ideally, the creators of revolution 5 will address this issue in future updates.