My experience is that a swivel socket (usually 9/16, if the bolts are USS, 15MM on metric bolts) on a long 3/8 extension will usually get on the nuts inside of the front crossmember. Usually just using a 3/8 swivel joint with a regular socket attached may not get you enough angle, you should try to have a swivel socket of the correct size, with the universal made into it. Socket pictured below:
If you can't get on the nuts through the lower control arm mounting holes with a swivel and extension. I have used a large step drill to make holes large enough for the swivel socket to fit through. The crossmember is plenty strong enough that a hole on both sides of the crossmember won't have any effect.