The spoilers will operate once the main gear trucks untilt. This assumes they are armed.
Forgive me if this is wrong (I'm not a jet pilot) but I recalled reading the following the other day..
Boeing 757 Flight Controls :: Spoilers & Speedbrakes
Speedbrakes AUTO Operation
On the ground, the speedbrake lever is driven aft to the UP position and the spoiler panels are fully extended, when either:
•there is hydraulic pressure to both Landing Gear truck tilt actuators and
•the landing gear is fully on the ground (both Truck Tilt Sensors not tilted) and
•both Thrust Levers are at idle or
•either reverse thrust lever is moved to the reverse idle detent.
The speedbrake lever does not need to be in the ARMED position for automatic operation to occur.