Melodeath
Moonbow
Options - Audio - Advanced: Under Playback & Recording, there's 'Record Pre-allocate File (seconds)'.
That might be what you're looking for? Not sure, I just record 2 bars before and chop it later. If I'm doing drums, I get em to stop at the end of each section (can sometimes be hard to get them to stop without hitting the crash on 1 tho).
I've seen the option before, but based on the manual, it doesn't seem like a Pre-record thing, so I never tried it.
Manual says: Record Pre-allocate File (seconds)--When this option is set to a value greater than zero, SONAR will pre allocate the file to be recorded to the size specified (in seconds). This means that the file will not be resized while recording until it reaches the allocated size. The setting has the potential to reduce disk activity while recording and allows for more possible tracks. The valid range is 0-14400 seconds and the default value is 0. A reasonable setting would be 10 minutes (600 seconds) to 30 minutes (1800 seconds).