There are things you can do, as a 3.5 player playing with 4.5 players (or for that matter anyone playing doubles with players much better than them). First, you want to put your partner in positions where he can win the point at net. This means getting first serves in (so he can poach), hitting returns crosscourt that dip at your opponent's feet (so he can poach), etc.
Second, and more importantly, you have to avoid the tendency every player has when playing with/against players better than them - trying to do too much. You are not going to impress them by hitting 1 out of 10 forehand returns down the line, even if that 1 winner was the best forehand you've ever hit. Attack the middle. Give your team a chance to win the point. Similarly, you are unlikely to ace a 4.5; and when you miss your 1st serve by 100 ft, the 4.5 will make you pay if your second serve is weak.
Finally, and consistent with above, swallow your ego. Don't get mad and swear when you make mistakes so other players will think you're "better" than the way you're playing. No one expects you to be 4.5. Instead, keep your head in the match, listen to your partner, and hustle your a s s off. Trust me, your partner will appreciate your effort and will also be more willing to play with you in the future.