You can bypass this restriction by applying it from your main character level 100 and mail it to your alt.
Here are the steps:
- Create the shoulder/leg on your level 100 toon.
- Apply the enchant.
- Send it to your alt.
ALSO: If your heirloom is upgraded to level 100, you will need to create it from a character below level 100, because the ilvl of the heirloom is 605 and the enchants are restricted to below ilvl 600.