If you have “been watching the Bandit for a while” (in your own words), then you’ll know how he/Phil does it. He has explained it in a few of his videos.
The Videoslots account was originally a UK account. After moving the account over to Malta, it was able to do bonus buys. The currency stays in £pound only because it was originally a UK account and Videoslots doesn’t change that. The Bandit uses remote desktop software on his own computer out to the Maltese computer (which also uses remote desktop, unattended access).
Chipmonkz does similar by having 2 addresses (UK and ROI). When in the UK, he remotes out to his ROI computer and therefore able to do bonus buys.