One other thing to remember is that characters aren't actually full adventurers until about level 5. Then at level 5 you have enough options in combat to really start playing with real monsters.
As a DM, I follow the rule of thumb that the highest encounter level you throw at a party is:
Level + (Demi Tier - 1) = Max encounter level
So if the group is level 4, that would be in the first Demi Tier (1 through 5) and so the highest level encounter I would throw at them would be a level four encounter.
4 + (1 - 1) = 4
If they were level 8, I could throw a 9 at them, etc.
I admit, I haven't tried this a upper Paragon or Epic tiers since the new math came out, so I don't know how well it will continue to play out.
In the end, though, your real problem seems to be you are in a party that is short two adventurers, and you have no Defender. Sometimes you can get away with no controller, and I could even see pulling a no striker, but leaders and defenders are both must haves, IMHO.
So long as you have that awesome cleric, I would probably make a Str/Wis Tempest Fighter with Whip Training [Multiclass] (Dragon 368) for weapon proficiency as well as the extra -2 penalty applied to enemy attacks.
And, I would go with a Minotaur with a Str 19, Dex 13, Wis 17. You would control a big area with a good chance to hit marking at least 2 targets a round (tempest can make 2 attacks with Dual Strike, and the Whip is prof 3, 1d4, off-hand, reach weapon, and the Tempest Technique gives you another +1 to hit if you are wielding off-hand weapons) giving those creatures a -4 to hit your friends (-2 from marking and -2 from the whip). Then rely on your cleric's healing abilities to keep him alive.
Don't worry about damage, because that is what the strikers are for, and your flat damage will outpace your variable damage rather quickly anyway.
Finally, give him a cowboy hat.
Especially if it
isn't a western setting.