We used to have this problem a lot, but in our case it was his oral skills that were lacking. You know the drill: "I know what must work from watching porn! I'll just keep doing this one thing for a while, and you'll orgasm so hard and be so proud of me for figuring this out!"
After often getting bored and faking it so we could get on with having sex, I eventually told him, and he actually came up with a wonderful idea. I had no experience with blowjobs, and didn't know where to start; he didn't know what the heck to do when going down on me. His plan: I'd lay back, and he'd start experimenting with as many different things as he could think of. He'd try each one for about 30 seconds, and I had to tell him if I liked it or not, or if it was closer to working. If it worked, he'd give me another minute (reward us, and so he'd remember), then move on. If it didn't work, he'd just move on. The next night, the table would turn and I'd experiment on him.
It wasn't the most amazing foreplay, and was a bit frustrating that one night, but it meant that all of a sudden, the next time he tried he was SO much better.
Giving feedback during sex can be really hard. You worry that it'll be a mood killer, or hurt someone's feelings, or you get impatient because damn it, you want that orgasm! When you change the expectations (this is a learning session, we're not immediately trying to have sex; we're learning each others' bodies so that next time is better), it becomes easier. You're expected to give feedback. You're not expecting it to be amazing. You're expecting false starts. It takes a lot of the performance pressure off, especially if you decide before hand that it's ok whether or not you move on to sex and orgasms after.
But after all that experimenting (with fingers, with a mouth, or with toys), we were usually ready to jump each other.