I think it will get supported in near future.
Until that happens you can use the following workaround in the cfg. Because Exit 2 is at the moment at door 1L, I made EXIT 2 to the preferred entry, removed exit 1 and exit 3. Now the passengers boarding at door 1L.
[exit1]
remove = 1
[exit2]
pos = -2.80 20.88 0.40 0.00
code = 11
name = Exit 2
embeddedStair = 0
[exit3]
remove = 1
