As a gross oversimplification you have three options
1) Find the nearest thing you can to a strong LOR from your current position and apply with that
2) Apply without any LOR from your current position
3) Wait long enough in your current position to develop a strong LOR there
Depending on the rest of your application package and your portfolio 1) or 2) could be feasible.
If you go with 2), how do you plan to explain the lack of an LOR from your current position?