What you're referring to is often called an oblique font, rather than an italic. An italic is a completely redrawn font that compliments the roman font. Historically, they were often VERY different from the roman, but modern italic are visually part of the same family.
Oblique fonts are essentially sheared romans. Older sans serifs used this approach. As you can see below, Helvetica Oblique and a sheared version of Helvetica Regular are visually identical.
However, be careful assuming ALL sans serifs have obliques rather than italics. Take a look at Myriad: its italic is custom drawn. The "s" is slightly different, and there's no way you'd get that nice "b" and "q" with a simple oblique.
All that to say, there are SOME typefaces you could modify like this. I myself have hesitantly have made an oblique Frutiger Condensed because no one has drawn one yet, to my knowledge. But proceed with caution!