I'd just do it, and if you ever get a tax audit, and they disagree, you'll just be asked (told) to refund what you owe.
If you want to be totally honest about it, just apportion an amount against your tax for the proportion of time you'd be using it for work and pleasure.
Something like 10% of time used for work, 90% used for pleasure. Then that would be 10% of the cost you could use for tax purposes.
Just stick a note in with your paperwork explaining that, so in five years time, you know what you did.
That's how I'd do it, but I'm not a tax accountant, and if I was using it for work for 10% of the time, that would seem fair to me.