kendrick in the mean time you might be able to use the `shell command` trick/hack in the custom algo to make a shell call to execute a special program to check for this. It would be a big hack, pretty messy, and would take a lot of creativity but it could be done as far as I see.
In general just make the script report back status codes which the algo would then read and act upon. On a large site you can pretty much expect it to run every minute. You would probably want to include some code so that your bot would only run say twice an hour and you would definitely not want it to block. And if something went wrong with it, you would want the algo to still be able to continue on gracefully.
So sample return status codes:
-3 = fatal error
-2 = queued, no data yet
-1 = transient error/timeout
0 = does not appear on site, no error
# = toplist position (If you wanted to go this far - would likely mean coding a handler for each site but it appears the TP algo has a variable for the domain name which you could pass to your bot)
And then your algo would act on these return codes.