Another approach is a recirculating delay line, google that. Probably not
practical for this problem.
Another approach is to make a simple UP based digitizer. If you used a PSOC
it has Vref, A/D, D/A, and memory, a simple low speed (1 MSPS) scope
front end could be made with maybe a very small number lines of code. Just
a thought.
Google "psoc oscilloscope". Most use an LCD for display, no reason you could not
use DAC and develop a trigger for your analog scope instead of LCD.
Regards, Dana.