Depending on his situation, it might be easier to build a table of known values for the constants and then just call sysconf anyway. As in:

# Untested, but the constants are right
use POSIX qw(sysconf);
$const{linux}->{_SC_NPROCESSORS_CONF} = 83; 
$const{aix}->{_SC_NPROCESSORS_CONF} = 71; 
print sysconf($const{$^O}->{_SC_NPROCESSORS_CONF});
[download]

If he's got more control over the target environment, he can use an h2ph-ish kind of tool to get them.