Discount Codes for Supporter Upgrade

Hi,

Anyone can suggest what is the best way to integrate discount codes for Supporter's upgrade?

For example, say the normal Supporter upgrade is $100 per year. Those with discount code ie. DISCODE can enjoy ie. 20% discount of $80 annual subscription instead.

I know E-Junkie supports discount management. Can E-Junkie be integrated into Supporter upgrade?

TYIA.

William