Can't hurt, right? I'd say, in general, manual stimulation and/or oral sex will help with erections. However, I can say from personal experience, if he's having trouble, trying harder might just be putting him on the spot. I'm perfectly healthy and have had trouble at various times in the past. This kind of thing really wears on your confidence.
In college i'd occasionally have erection trouble while drunk. Ok, this is normal. I did not do much hooking up at all during college, or high school for that matter (darn catholic guilt). When I got out of college, I was dating a girl, and would lose the erection when it was time for sex. All mental. We broke up. It took a lot of time, and another girl to work that out. I still occasionally get worried about that. Happened recently with a new girl, although I don't think that was mental (very tired and hung over). However, we're probably going to have sex for the first time today or tomorrow, and that old worry is in the back of my mind.
So, in short, not being able to get an erection is a big deal for a guy, so trying harder might not help. There's a medical reason, but the mental reason is there too. I'd suggest doing the manual and oral thing, but not specifically in preparation for sex. Just suggest relaxing in bed one afternoon, maybe with the tv on, or some music or whatever. Just start playing around and see what happens.
Any more detail on the health issue or medication? Maybe some timing should be involved? Like if he takes the medication once a day, try when its wearing off, not when its at its strongest? You know? Maybe try the morning, or right after work, the middle of the night? Something different.
