Hmmm, well you certainly could try to retrofit the certificate 1.8 activity locking code to the certificate for 1.7. However, I think it would be a better use of your time to try to get your SCORMs to work. For one thing, you really don't want to be stuck with Moodle 1.7 forever. And, there are lots of nice new features in 1.9, particularly better grade reports.
First, you should install the latest 1.9+ version in a test site and try your SCORMS. Be sure to turn debugging to the highest level in admin settings to see if you get any error messages with the SCORMs, then look through the SCORM forums for more info. I've tested SCORMS created by several different programs in 1.9 and have not had any problems.