For an internal caller , the only option is to use back to back trunks - messy but it can be done .
I once had to use LCR to send a call out via pstn trunks which were direct connected to analog extensions
caller dials 600 - sent to lcr - dont strip any digits and route to the pstn trunks , pstn trunk goes off hook which takes the analog off hook and dials 600
600 was a UCD pilot with an announcement .
- Obviuosly this only supports as may trunks as you have and its messy and prone to trunk lockups .
If I never did anything I'd never done before , I'd never do anything.....