NLHE: Facing 2+ Limpers w/ Marginal Holdings

Anyone have any thoughts/suggestions for playing marginal cards against multiple limpers? My basic approach to pre-flop play has been raise/fold. The only hands that I would limp behind with being small pairs and SC's. In HOH Cash Games, Harrington suggests NOT attacking limpers with less than TT+ and AQs. So, I'm a little confused about middling hands...

Say you're in middle position behind 2-3 limpers and you hold:

AJo
99-77
KQo

Do you limp behind or put in the raise???

It depends on my own position and the likelihood that I'll be playing OOP with a marginal hand (such as 77). As a general rule, I try to isolate limpers with most hands that I would be opening the button with (so AJ, KQ, 99, etc.), and try to take the pot down postflop (unless I flop huge, in which case I try to win a big pot, obviously.)

depending on their position on the table ichange my play. someone acting first who usually calls might have a monster qq kk aa and is looking for a bet to reraise the person. if acting later on i might throw out a reraise