Well then as I see it regular expressions are your only option.
You can use this single regex which is tailored to your needs:
if ($regex($1-,/(^|[^\.\d])0*[1-9]|\.[5-9]/S)) {
Or you can identify and loop over all numbers (I like this regex even less):
var %large, %i = $regex($1-,/(\d*(?:\.\d+))/Sg)
while (%i) {
if ($regml(%i) >= .5) { %large = 1 | break }
dec %i
}
if (%large) {