This will not work if your stem bolt has a nut on the end rather than a threaded insert in the casting but if your stem is suitable it helps.
Take the bolt out of the stem.
Insert the bolt from the reverse side until it just starts coming through the small gap between the two halfs (if you get what I mean).
Place a five pence peace in the the gap and carry on screwing the bolt in.
This will allow you to spread the stem open slightly. Obviously do not try and open up the stem too far as it is aluminum but it leaves you hands free from having to use a screw driver in one hand.
This will not work if your stem bolt has a nut on the end rather than a threaded insert in the casting but if your stem is suitable it helps.
Take the bolt out of the stem.
Insert the bolt from the reverse side until it just starts coming through the small gap between the two halfs (if you get what I mean).
Place a five pence peace in the the gap and carry on screwing the bolt in.
This will allow you to spread the stem open slightly. Obviously do not try and open up the stem too far as it is aluminum but it leaves you hands free from having to use a screw driver in one hand.