You can give your formats different names, and open FILEHANDLES with those names to STDOUT then use those names as parameters to write. ie:

open FORM1, ">-" or die "Error: $!\n";
open FORM2, ">-" or die "Error: $!\n";

format FORM1 =
FOO      BAR
@<<<<<<< @<<<<<<<
$foo, $bar
.

format FORM2 =
FOOBAR BAR
@<<<<< @<<<<<<<
$foobar, $bar
.


write FORM1;
write FORM2;
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