Traditional telephone companies have long allowed customers to dial 11xx rather than *xx on most feature codes - originally this was put in place for rotary dial phones that didn't have * on the dial. But with VoIP, there is another use - to bypass built-in feature codes in some adapters. For example, in the Sipura/Linksys adapters, *70 means cancel call waiting for the next call only, whereas in FreePBX it is used to enable call waiting. If there were a checkbox on the page that would simply allow the use of 11xx in addition to *xx, then Sipura adapter users could be instructed to dial 11xx to turn on call waiting (after which *70 on their adapter should work as expected).
So my suggestion is, put a checkbox near the bottom of the Feature codes pages that says:
 Allow user to replace * with 11 at start of feature codes.
And if that box is checked, make it so that either code will manipulate the feature.
I do realize that as a stopgap you can set up a custom extension (example, make a custom extension 1170 and put Local/*70@from-internal in the Dial field) but it would be rather cumbersome to do that for all the feature codes.