As an alternative to the pipe script solution, you can change your .conkyrc by adding a dummy element and using i3bar's separator properties:
,{ \
"full_text": "Last Element", \
"separator": false, \
"separator_block_width": 50 \
} \
,{ \
"full_text": "" \
} \
The 50 will change the widht of the gap to the right. Of course, instead of using separator_block_width you can also just use spaces in the dummy element's full_text property. You'll still need separator: false, though.
One advantage to is that you don't need another shell level in your chain.
By the way: the \ are used to turn the JSON into one physical line which improves the performance of i3bar's parsing by quite a bit.