Hello,
You can still contact a third party developer or one HikaShop partner.
If you choose that solution ; the best would be to use "product custom field" in order to store the text that you want to display in the button.
The result will be "less dynamic" than loading the characteristic but it will not impact the page rendering and (most important point), it will require less development time (so it will be cheaper for you).
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.