I don't have any tool at the moment.. I do it manually... Not very clever...
When searching on internet, I found these ideas:
1) Tape 2 pencils together for 1/4" seam allowance! this is so clever..
|Picture from five green acres|
You could also pay for something called Seam Tracer which hold 2 pencils together:
There is also something like these which you could use to add seam allowance.
3) Seam Allowance Guide by Hollie
Adding seam allowance automatically while you cut...
Anyone interested to get this tool? It is sold at AUD15 (and add AUD3 for international postage), but if we have 10 people we could get it at better price. Let me know if you are interested...
( Please email me (anic dot khow at gmail dot com) if you would like to get one, special price is only for Malaysian customers.)