Have we asked WHY the OP can't use external antennas? A VHF mag mount is not exactly a huge inconvenience, and MURS with a 1/4 wave whip will do 2-3 miles without breaking a sweat.
As for the usual handwringing about using non-type accepted radios: get over it. The agency which is the sole authority on this issue has declined to ever prosecute anyone for using a removable antenna on FRS or 5W on MURS. That means they don't care. A decision on the part of the regulatory body to uniformly not enforce is effectively identical to something being legal. Extra-obeying a law doesn't make you more virtuous or more right or in fact accomplish anything at all, and these cases of not complying with the law can not POSSIBLY cause harm to anyone that obeying the strict letter of the law would not already have caused.
Would you also tell someone to make sure they never carry wire cutters across county lines in Texas? Because that's a felony, but it also painfully obvious that it is not a violation of lawful behavior to do so, and no one has even been arrested for it, let alone prosecuted, since I have been alive.
If you cannot, by going up to a peace officer and both declaring and demonstrating the violation of MURS or FRS or even GMRS regulations, get arrested, it's not really illegal. Just like the wire cutters, declining to enforce is indistinguishable in every way from declaring it legal, and things which cannot be distinguished are the same.
As for the WELL IF YOU BREAK ONE LAW YOU WOULD BREAK ANOTHER argument, that is complete hogwash and you're a damn fool for saying it.
People speeding doesn't increase their likelihood to do murder, because those are obviously not equivalent in any way. To claim otherwise is absolute lunacy, and that's what's happening here.
Imagining that emitting three extra watts of a frequency that doesn't propagate harms the social order or is morally bankrupt or, most ridiculously, will land you in the hoosegow, is just plain stupid.
Get over yourselves. This isn't people running two kilowatts on CB or operating on ham bands unlicensed. That which cannot be demonstrated to cause harm, is not harm, and the only legitimate purpose of the law is to prevent harm.