Step 1: Get a second back wheel - geared axle.
The image here of a geared back wheel does not have a freewheel. The freewheel is the part with five or six gears on it that can only apply force in one direction.
Step 2: Problem Solving
The back wheel is typically around six inches, the front is five.
To solve this problem, you need a bolt or an axle from the rear wheel.
And you need some luck and the correct front axle fork.
The correct axle fork is one that can be stretched, not all can be stretched outwards to accommodate a wider axle..
1)Bolt one side of the axle to the side of the front fork. Two lock nuts.
2)On the other side "loosen" a third nut outwards towards the other side. This will stretch the metal frame of the fork.
I don't have a picture of these steps , I will add them later when I have time.
DANGER When you are putting pressure on the fork, it will try to push out of the slot. It may pop out suddenly so watch your fingers and eyes.
The turning will take so time be patient, and you might have to do it a few times as the third bolt you are turning outwards tends to slip out.
When to stop
With a measuring tape, check on the distance between the front fork from time to time.
Its static distance size can be stretched a bit (about a half inch) so when measuring it does NOT have to be the exact size wide of the rear axle.