Too late for me but I can’t resist to write that for Flex Overdub you just have to record the Flex track playing it :
ABCD inputs + T1 or T2, T3…Cue
or
different combinations even with Main but beware of feedbacks, or go with them for pitch delays !
More details if needed later. Try before. 
Hello, new Octatrack user here. I have a question that maybe one of you can answer about pickup machines… Say I have a drum beat at 120 bpm and I want to record a loop without having the Octatrack change the tempo and instead stick to the tempo I already have playing. Is there a way to do that? Thanks for you time
You would turn off timestretch, right?
How might a fellow go about doing this?
The first PU machine will (afaik) always change the tempo. Luckily you can set it up to change to your current tempo (so no actual change) by quantising the recording start and length.
pretty sure this is the answer.
You have to use QREC and QPLAY (Rec Setup 2). A value 16 quantize rec / play to a bar for example. PLEN=Pattern Length.