I think you can disable the reverse just as you can with most reversible speedos - connect positive lead to motor directly from battery and leave the motor "+" coming from speedo disconnected. That is, connect the thing as you would with any non-reversible 3-lead competition ESC and isolate the 4th (motor +) lead of ESC. This has worked with more ESCs than I can remember. You'll still have brakes and as a bonus the ESC resistance will be half of original (as the "+" row of FETs is not used). Note: this does not mean the ESC will handle double the current!
The reason why this works is that most of reversible ESCs have the same logic as fwd/brk ESCs - during most of the time motor+ is directly connected to battery+, gas and brakes are done by changing the voltage on motor- lead (negative for gas, positive for brakes). For reverse the motor+ lead is just switched from full+ to full-, so if you don't use this lead, but connect + to motor directly from battery, bingo, no reverse.
I can't guarantee that all ESC's work like that, but it has worked on all I've tried (>10 different over the years). Anyway, it won't do any harm, even if it doesn't work, so it's worth to try.
About setup- I think you can download the user manuals at http://www.lrp-electronic.de/