there is an option. hire an expert.
someone who'd probably let your script run it's course, somehow getting a timestamp for time critical stuff (posts, topics, pms -- essentially everything that you MUST preserve)
then after the import, close the board for a short period to grab all the stuff that wasn't gotten after the import.
it's more than that though, because you wouldn't only be searching for NEW things that have been added.. but also things that might have been deleted in that time period as well.
in short, it's messy, but with care the transitional process could be mitigated to an acceptable data transformation.
bottom line: if you want your board to be imported 'as is' , then close it for half the day and just let it rip. otherwise hire someone to get you as close as is reasonable, while you let the board be 'live'. i'd lean toward board closure and save yourself what it costs to hire it done.. but that's just me.
below botton line: also keep in mind that importing while the board is live can cause problems too.. ie: consider that you might import a topic ID, but not the posts, since they are asyncronous.. or vice versa.. not good
