No one will think you’re trying to cheat if you single-space poems in a novel-in-verse submission. Agents and editors want samples in order to assess the project, and assessment of a novel in verse usually requires more than a few poems. It’s an exceptional format. Stick to 12-pt font and regular margins so as not to distract from the content, then single-space the poems and see how many fit onto 10 pages. You may not fit a full 10 poems, but this isn’t about subbing one 10 for another. Nor is it about rules. The 10-page standard is meant to manage workflow and avoid the costs and physical manipulation of mailing, printing, and lugging full manuscripts. Even with email submissions, we keep the 10-page standard because that’s enough for the initial assessment and there can still be printing and lugging. You can state at the end of your query letter that you’re sending 10 pages with [#] poems single-spaced to offer them a useful sample. They’ll see you aren’t being sneaky but rather are being thoughtful about the process. Stay true to the spirit of standard formatting and you’ll be fine.