I'm not sure I follow, how does using a reservoir mean wasted water (except for the evaporation from the reservoir, but really this is minimal compared to the tank..) ??
Danny, I really have to say this, but get a reservoir on there pronto!! Don't debate, just do it!
Hooking the RO/DI directly to the float valve is going to lead to premature RO membrane failure. When I moved into my current house in 2004, I hooked my RO/DI directly to the sump like that. That constant on/off cycles are murder on the membranes. I went through 3, maybe even 4 membranes in the first year before I realized why they were failing. Since hooking up the reservoir (and filling the reservoir manually), I haven't had to replace a membrane yet (at least two years on this membrane).