I have a set of tora's without the necessary poplock to lock out the forks. They seem to be expensive to buy, can I just use an old thumbie for this job, sorry if this is self evident.....
That might work. Be careful not to pull it too far though.
Thumbies pull a lot more cable than the poplock lever, and I'm not sure how the internals would hold up if you turn them too far.
I did this with a £2.89 plastic shimano thumb shifter from eBay.
When you set it up just make sure you leave a bit of slack on the cable so that even if you yank the shifter all the way round then you'll not get too much travel.