Well, you can't really attach a satchel to a vehicle. You can place it near one on the ground... Luckily, there are ways around this
If you know what tank you're planning to attach a sticky bomb to, then creating a script for it would be easy. First just add an action to the tank:
myTank addAction ["Attach Sticky Bomb","scripts\stickyBomb.sqs"]
Then,
stickyBomb.sqs would look like this:
;stickyBomb.sqs
;Tank that the action is attached to.
_tank = _this select 0
;Action number to remove
_indexNumber = _this select 2
;Give the player 10 seconds to run away.
~10
;Get the position of the tank
_tankPos = getPos _tank
_tankX = _tankPos select 0
_tankY = _tankPos select 1
;Create a large explosion at the tank.
_stickyBomb = "LaserGuidedBomb" camCreate [_tankX,_tankY,1]
;Make sure he's dead :)
if (alive _tank) then {_tank setDammage 1}
;Remove the now redundant action
_tank removeAction _indexNumber
;exit script
exit
And walla! You have it! Just put that script in side a folder called "scripts" inside your mission directory.
If you want to add it to multiple tanks, then it gets a little more complicated... but hopefully that will work for now.