No need to decrease injection; just switch to HCG for 3 weeks to restore the testes to full size and function and then 4 weeks of PCT. Clomid will work for that.
wk 1-3: HCG - 500IU EOD for 20 days (5,000 IU total)
wk 4-7: Clomid 50mg/day
The only information you gave is that he was on way too long but what I recommended is probably the best he can do regardless. He can expect a period of lethargy, depression, and erectile disfunction during wks 4-7 while his HPTA is recovering and his testosterone is low. Without the HCG, this period would last even longer.
The clomid only hastens the recovery of testosterone production, it doesn't make up for it. In fact, it can make you emotional and weepy like a girl PMSing. Viagra can help with the ED but the rest you pretty much have to tough out.
There are other, newer PCT products available through sponsors of this board (such as Unleashed) that can be used in place of the clomid. However, I don't have any experience with them.
Be prepared for the emotional side effects though; they will be profound. It's not easy to go from feeling like Superman to the complete opposite in just a few weeks.