They could be converted, but it won't be very simple. Probably easier to just use a home made 2 meter antenna, but that's what you're thinking of isn't it.
If the fiberglass antennas are spirally wound (most likely), at the very least it would mean finding the correct length regarding the inductance of those coils. That would be much shorter than commonly thought, and not really all that 'productive'. And then you get to deal with finishing off that fiberglass part.
Probably, using the base ferrules and mount, then adding a 19" whip would yield about as good as anything. One aspect is that any 11 meter sized antenna has to be more 'heavy duty' than a typical 2 meter antenna, they're just bigger, you know? If that aspect doesn't bother you, then so what. And then you'd miss out on all that 'messing' around getting the thing to work. Or, build a small matching coil and fiddle around with the taps till it/they work. Whatever, do it, do it!
- 'Doc
Come to think about it, what's an 'OutBacker' but a helically wound antenna with a 'tap' lead to use the necessary helical coils as a loading coil?