Have a binding for ButtonPress that sets a flag variable, as well as one for ButtonRelease that clears the flag. Then, have a binding for Motion that returns immediately if the flag is not set, otherwise processes the event normally. Something like:

my $flag = 0;
$cnv_reference_ref->bind("location$x", '<B1-ButtonPress>' => [sub { $f
+lag = 1 }, "$i", "1"]);
$cnv_reference_ref->bind("location$x", '<B1-ButtonRelease>' => [sub { 
+$flag = 0 }, "$i", "1"]);
$cnv_reference_ref->bind("location$x", '<B1-Motion>' => [sub { return 
+unless $flag; click_select(@_) }, "$i", "1"]);
[download]