Right, I said it was easy and these instructions make it seem totally crazy, but I promise once you’ve done it it’s trivial 
SETUP
Start with a new project. This is a complete set of instructions, you shouldn’t need to do anything else at all to get this to work:
Change the machine to FLEX on T1
Select the R1:RECORDING1 buffer for T1
Press FUNCTION > A/B and set:
INAB to A B
IN C/D to - Note: this process works exactly the same for inputs CD too!
RLEN to MAX
TRIG to ONE2 - this means you press once to start and a second time to stop.
LOOP to ON
Press FUNCTION > C/D and set:
FIN to 0.063
FIN to 0.063
AB to 127
QREC to PLEN
QPL to OFF
CD to 0
Setting QREC to PLEN means:
- the recorder will start recording after the current pattern plays to the end
but also
- the recorder will stop recording, on a second press, after the current pattern plays to the end.
What might not be obvious about this is that if the recording is MAX and the record length (allocated memory - let me know if you need more info on this) is changed in the settings, you can effectively record as many bars as you like (remember memory setings!! Default is about 16 seconds but you can increase this so you can record whole songs if you like) and always end recording quantised at the end of the pattern.
You could do the same thing by setting the PLEN to a number of beats - so if you wanted you could just set it to 4 and then you just have to activate recording in the bar before you want recording to start & same for stop. The important thing to note is that you are quantizing the start and stop of the recording, not the recording itself.
RECODING PROCESS
Hold T1 & press Rec A/B and recording starts after the current PLEN plays to the end.
Record as many bars as you like.
Hold T1 & press Rec A/B and recording stops after the current PLEN plays to the end.
If you like, you can double press T1 then FUNCTION + BANK then PLAYBACK to watch the file being recorded.
PLAYBACK
Press NO so that you’re back at the default screen.
Make sure T1 is still selected.
Press COPY to enter edit mode
Press FUNCTION and TRIG1 - this adds a oneshot trig that is armed and ready to play back your sample next time the pattern loops.
From that point forward you just need to ARM T1 to get the sample to play back from the beginning.
Note, the sample will continue to play indefinitely.
Interesting things happen with AMP > HOLD and AMP > REL when you have extra long loops like this - worth a look!
To answer the OP - it’s not possible to stop recording using a trig and get the same effect.
Have fun!!