Depending on how much extra tube you have (and the type of bike), you might consider just stacking up some spacers, and running it as-is.
In my slower, antiquated state, I now prefer a bit more of an upright position, anyway, so it often works out OK.
On a recent project, I scored a pack of six 10mm alu spacers pretty cheap from a Amazon vendor, which fixed me right up.
Otherwise, as I understand, a hacksaw jig is the way to go, for a DYI job.