|I ran across this tip in Sandra Betzina's Power Sewing Step-By-Step recently. I wasn't looking for it, but found it just when I needed it:
Sandra suggests that if you can't find a suitable sew-in interfacing, you can underline the garment with a lightweight cotton (such as batiste or lawn) and then fuse the interfacing to the underlining.
When I applied this technique I did it slightly differently. Instead of underlining the garment, I first fused the interfacing to the uncut batiste, then cut it out and treated it like sew-in interfacing.