> *clocked at 1MHz*

Assuming that you might be interested in anything up to 10 harmonics of 1 MHz, the wavelength of 10 MHz is 30 metres and, the rule of thumb is that anything longer than about one-tenth of a wavelength is going to potentially be problematic.

> *What is the best way to handle this in your opinion?*

Hence, 3 metres isn't really going to pose a problem to either the data down the stub (30 cm) or the original data path (10 cm). If in doubt, connect to the stub via 1 kΩ resistors and use a differential amplifier to monitor the data signal.