The Case-Church Amendment and War Powers Act made it tough for President Ford to support South Vietnam.
Suppose these restrictions included a few loopholes. One, if the Vietnam cease-fire was violated before 3 years the ink of the treaty dried, the president is capable of unilaterally supporting South Vietnam. Two, more raid is funneled down South Vietnam's throat (say 3.3 billion worth of equipment and ammo annually instead of 700 million but same amount of fuel aid as OTL). Three, Senate can give approval for an administration to give further action against anyone who violates a treaty co-signed by America.
North Vietnam started their Central Highlands offensive before the 3 years after the Paris agreement
http://en.wikipedia.org/wiki/Battle_of_Ban_Me_Thuot which is a pretty blatant violation of the cease-fire.
Under the loopholes, Ford can order America back into Vietnam. Since he wants to get re-elected, he will obviously NOT do that.
But this does create the possibility of offering B-52 bombing and Naval Gunfire support to help the South Vietnamese. North Vietnam in the past year created a network of roads, supply depots, and forest clearings for their armored vehicles and these were vulnerable to bombings unlike the smaller-capacity Ho Chi Minh trail (which was meant for hand porting not vehicle use is some sections). A carpet bombing on a few of these obviously visible trails would create a bunch of craters that prevent movement.
The speed of the Ban Me Thout offensive required vehicles. Sure the North Vietnamese could go into the jungle where American airpower can't hit them without spotters, but that screws up their timetable badly.
Also in OTL a problem the South Vietnamese had was logistics. The number of bombing sorties in Ban Me Thout was 1/30 of as many as they would have flown if decided by tactics instead of fuel. OTL one bomb hit a division HQ by accident and everything went downhill from there, but if that is butterflied away, more bombs dropped hopefully would hit enemies not allies. Artillery no longer had HEAT rounds, illuminating shells, or flares. Mortar shells were running out. LAW and TOW ammo were gone. The M-16 was a maintenance problem (something about needing cleaning oils or whatever) so much that many soldiers in 1974 bought M-14s and ammo rom Tailand or used captured AK-47s. Chinooks were badly needed for spare parts and was the most critical. Even unarmored trucks were in short supply of spare parts, meaning units were nailed close to their deployment zones.
I obviously don't think Ford would go for the full intervention. But Nixon gave his personal promise a violation of the cease-fire agreement would be met with "severe consequences" and TTL loopholes allow that.