I think the only way to detect overflow of TMR0 per se is to poll TMR0. For example, a "movf TMR0,w" or its equivalent in C should set the zero flag in STATUS (i.e., STATUS,2) when the timer rolls over. I have not actually tried that, though. Running it at 1:1 may be more difficult.
If you want counts less than 256, then you can do presets or various subtractions or additions to determine the actual count. At each rollover, you need to repeat any presets.
John